1
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Fransson T, Pettersson LGM. TDDFT and the x-ray absorption spectrum of liquid water: Finding the "best" functional. J Chem Phys 2024; 160:234105. [PMID: 38884399 DOI: 10.1063/5.0209719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Accepted: 06/03/2024] [Indexed: 06/18/2024] Open
Abstract
We investigate the performance of time-dependent density functional theory (TDDFT) for reproducing high-level reference x-ray absorption spectra of liquid water and water clusters. For this, we apply the integrated absolute difference (IAD) metric, previously used for x-ray emission spectra of liquid water [T. Fransson and L. G. M. Pettersson, J. Chem. Theory Comput. 19, 7333-7342 (2023)], in order to investigate which exchange-correlation (xc) functionals yield TDDFT spectra in best agreement to reference, as well as to investigate the suitability of IAD for x-ray absorption spectroscopy spectrum calculations. Considering highly asymmetric and symmetric six-molecule clusters, it is seen that long-range corrected xc-functionals are required to yield good agreement with the reference coupled cluster (CC) and algebraic-diagrammatic construction spectra, with 100% asymptotic Hartree-Fock exchange resulting in the lowest IADs. The xc-functionals with best agreement to reference have been adopted for larger water clusters, yielding results in line with recently published CC theory, but which still show some discrepancies in the relative intensity of the features compared to experiment.
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Affiliation(s)
- Thomas Fransson
- Department of Physics, AlbaNova University Center, Stockholm University, 10961 Stockholm, Sweden
| | - Lars G M Pettersson
- Department of Physics, AlbaNova University Center, Stockholm University, 10961 Stockholm, Sweden
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2
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Jangid B, Hermes MR, Gagliardi L. Core Binding Energy Calculations: A Scalable Approach with the Quantum Embedding-Based Equation-of-Motion Coupled-Cluster Method. J Phys Chem Lett 2024; 15:5954-5963. [PMID: 38810243 DOI: 10.1021/acs.jpclett.4c00957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2024]
Abstract
We investigated the use of density matrix embedding theory to facilitate the computation of core ionization energies (IPs) of large molecules at the equation-of-motion coupled-cluster singles doubles with perturbative triples (EOM-CCSD*) level in combination with the core-valence separation (CVS) approximation. The unembedded IP-CVS-EOM-CCSD* method with a triple-ζ basis set produced ionization energies within 1 eV of experiment with a standard deviation of ∼0.2 eV for the core65 data set. The embedded variant contributed very little systematic error relative to the unembedded method, with a mean unsigned error of 0.07 eV and a standard deviation of ∼0.1 eV, in exchange for accelerating the calculations by many orders of magnitude. By employing embedded EOM-CC methods, we computed the core ionization energies of the uracil hexamer, doped fullerene, and chlorophyll molecule, utilizing up to ∼4000 basis functions within 1 eV from experimental values. Such calculations are not currently possible with the unembedded EOM-CC method.
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Affiliation(s)
- Bhavnesh Jangid
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Matthew R Hermes
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
| | - Laura Gagliardi
- Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, United States
- Pritzker School of Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States
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3
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Folkestad S, Paul AC, Paul née Matveeva R, Reinholdt P, Coriani S, Odelius M, Koch H. Quantum Mechanical Versus Polarizable Embedding Schemes: A Study of the Xray Absorption Spectra of Aqueous Ammonia and Ammonium. J Chem Theory Comput 2024; 20:4161-4169. [PMID: 38713524 PMCID: PMC11137810 DOI: 10.1021/acs.jctc.4c00105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 04/16/2024] [Accepted: 04/17/2024] [Indexed: 05/09/2024]
Abstract
The X-ray absorption spectra of aqueous ammonia and ammonium are computed using a combination of coupled cluster singles and doubles (CCSD) with different quantum mechanical and molecular mechanical embedding schemes. Specifically, we compare frozen Hartree-Fock (HF) density embedding, polarizable embedding (PE), and polarizable density embedding (PDE). Integrating CCSD with frozen HF density embedding is possible within the CC-in-HF framework, which circumvents the conventional system-size limitations of standard coupled cluster methods. We reveal similarities between PDE and frozen HF density descriptions, while PE spectra differ significantly. By including approximate triple excitations, we also investigate the effect of improving the electronic structure theory. The spectra computed using this approach show an improved intensity ratio compared to CCSD-in-HF. Charge transfer analysis of the excitations shows the local character of the pre-edge and main-edge, while the post-edge is formed by excitations delocalized over the first solvation shell and beyond.
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Affiliation(s)
- Sarai
Dery Folkestad
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
| | - Alexander C. Paul
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
| | - Regina Paul née Matveeva
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
| | - Peter Reinholdt
- Department
of Physics, Chemistry and Pharmacy, University
of Southern Denmark, SDU, Campusvej 55, 5230 Odense, Denmark
| | - Sonia Coriani
- Department
of Chemistry, Technical University of Denmark,
DTU, Kemitorvet Bldg 207, 2800 Kongens Lyngby, Denmark
| | - Michael Odelius
- Department
of Physics, Stockholm University, 10691 Stockholm, Sweden
| | - Henrik Koch
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
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4
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Folkestad SD, Paul AC, Paul Née Matveeva R, Coriani S, Odelius M, Iannuzzi M, Koch H. Understanding X-ray absorption in liquid water using triple excitations in multilevel coupled cluster theory. Nat Commun 2024; 15:3551. [PMID: 38670938 PMCID: PMC11053016 DOI: 10.1038/s41467-024-47690-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 04/03/2024] [Indexed: 04/28/2024] Open
Abstract
X-ray absorption (XA) spectroscopy is an essential experimental tool to investigate the local structure of liquid water. Interpretation of the experiment poses a significant challenge and requires a quantitative theoretical description. High-quality theoretical XA spectra require reliable molecular dynamics simulations and accurate electronic structure calculations. Here, we present the first successful application of coupled cluster theory to model the XA spectrum of liquid water. We overcome the computational limitations on system size by employing a multilevel coupled cluster framework for large molecular systems. Excellent agreement with the experimental spectrum is achieved by including triple excitations in the wave function and using molecular structures from state-of-the-art path-integral molecular dynamics. We demonstrate that an accurate description of the electronic structure within the first solvation shell is sufficient to successfully model the XA spectrum of liquid water within the multilevel framework. Furthermore, we present a rigorous charge transfer analysis of the XA spectrum, which is reliable due to the accuracy and robustness of the electronic structure methodology. This analysis aligns with previous studies regarding the character of the prominent features of the XA spectrum of liquid water.
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Affiliation(s)
- Sarai Dery Folkestad
- Department of Chemistry, Norwegian University of Science and Technology, NTNU, 7491, Trondheim, Norway
| | - Alexander C Paul
- Department of Chemistry, Norwegian University of Science and Technology, NTNU, 7491, Trondheim, Norway
| | - Regina Paul Née Matveeva
- Department of Chemistry, Norwegian University of Science and Technology, NTNU, 7491, Trondheim, Norway
| | - Sonia Coriani
- Department of Chemistry, Technical University of Denmark, DTU, 2800, Kongens Lyngby, Denmark
| | - Michael Odelius
- Department of Physics, Stockholm University, 10691, Stockholm, Sweden
| | - Marcella Iannuzzi
- Department of Chemistry, University of Zurich, 8057, Zürich, Switzerland
| | - Henrik Koch
- Department of Chemistry, Norwegian University of Science and Technology, NTNU, 7491, Trondheim, Norway.
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5
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Arias-Martinez JE, Wu H, Head-Gordon M. Generalization of One-Center Nonorthogonal Configuration Interaction Singles to Open-Shell Singlet Reference States: Theory and Application to Valence-Core Pump-Probe States in Acetylacetone. J Chem Theory Comput 2024; 20:752-766. [PMID: 38164934 DOI: 10.1021/acs.jctc.3c01139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
We formulate a one-center nonorthogonal configuration interaction singles (1C-NOCIS) theory for the computation of core excited states of an initial singlet state with two unpaired electrons. This model, which we refer to as 1C-NOCIS two-electron open-shell (2eOS), is appropriate for computing the K-edge near-edge X-ray absorption spectra (NEXAS) of the valence excited states of closed-shell molecules relevant to pump-probe time-resolved (TR) NEXAS experiments. With the inclusion of core-hole relaxation effects and explicit spin adaptation, 1C-NOCIS 2eOS requires mild shifts to match experiment, is free of artifacts due to spin contamination, and can capture the high-energy region of the spectrum beyond the transitions into the singly occupied molecular orbitals (SOMOs). Calculations on water and thymine illustrate the different key features of excited-state NEXAS, namely, the core-to-SOMO transitions as well as shifts and spin-splittings in the transitions analogous to those of the ground state. Simulations of the TR-NEXAS of acetylacetone after excitation to its π → π* singlet excited state at the carbon K-edge, an experiment carried out recently, showcase the ability of 1C-NOCIS 2eOS to efficiently simulate NEXAS based on nonadiabatic molecular dynamics simulations.
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Affiliation(s)
- Juan E Arias-Martinez
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, United States
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Hamlin Wu
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Martin Head-Gordon
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, United States
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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6
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Dey S, Folkestad SD, Paul AC, Koch H, Krylov AI. Core-ionization spectrum of liquid water. Phys Chem Chem Phys 2024; 26:1845-1859. [PMID: 38174659 DOI: 10.1039/d3cp02499g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
We present state-of-the-art calculations of the core-ionization spectrum of water. Despite significant progress in procedures developed to mitigate various experimental complications and uncertainties, the experimental determination of ionization energies of solvated species involves several non-trivial steps such as assessing the effect of the surface potential, electrolytes, and finite escape depths of photoelectrons. This provides a motivation to obtain robust theoretical values of the intrinsic bulk ionization energy and the corresponding solvent-induced shift. Here we develop theoretical protocols based on coupled-cluster theory and electrostatic embedding. Our value of the intrinsic solvent-induced shift of the 1sO ionization energy of water is -1.79 eV. The computed absolute position and the width of the 1sO peak in photoelectron spectrum of water are 538.47 eV and 1.44 eV, respectively, agreeing well with the best experimental values.
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Affiliation(s)
- Sourav Dey
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
| | - Sarai Dery Folkestad
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
| | - Alexander C Paul
- Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway
| | - Henrik Koch
- Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway
| | - Anna I Krylov
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.
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7
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Davis MC, Garrett NR, Fortenberry RC. F12+EOM Quartic Force Fields for Rovibrational Predictions of Electronically Excited States. J Phys Chem A 2023. [PMID: 37235692 DOI: 10.1021/acs.jpca.3c00072] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Quartic force fields (QFFs) constructed using a sum of ground-state CCSD(T)-F12b energies with EOM-CCSD excitation energies are proposed for computation of spectroscopic properties of electronically excited states. This is dubbed the F12+EOM approach and is shown to provide similar accuracy to previous methodologies at lower computational cost. Using explicitly correlated F12 approaches instead of canonical CCSD(T), as in the corresponding (T)+EOM approach, allows for 70-fold improvement in computational time. The mean percent difference between the two methods for anharmonic vibrational frequencies is only 0.10%. A similar approach is also developed herein which accounts for core correlation and scalar relativistic effects, named F12cCR+EOM. The F12+EOM and F12cCR+EOM approaches both match to within 2.5% mean absolute error of experimental fundamental frequencies. These new methods should help in clarifying astronomical spectra by assigning features to vibronic and vibrational transitions of small astromolecules when such data are not available experimentally.
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Affiliation(s)
- Megan C Davis
- Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
| | - Noah R Garrett
- Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
| | - Ryan C Fortenberry
- Department of Chemistry & Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
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8
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Datar A, Gudivada S, Matthews DA. Ab Initio Investigation of Intramolecular Charge Transfer States in DMABN by Calculation of Excited State X-ray Absorption Spectra. J Phys Chem A 2023. [PMID: 37209154 DOI: 10.1021/acs.jpca.3c01409] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Dual fluorescence in 4-(dimethylamino)benzonitrile (DMABN) and its derivatives in polar solvents has been studied extensively for the past several decades. An intramolecular charge transfer (ICT) minimum on the excited state potential energy surface, in addition to the localized low-energy (LE) minimum, has been proposed as a mechanism for this dual fluorescence, with large geometric relaxation and molecular orbital reorganization a key feature of the ICT pathway. Herein, we have used both equation-of-motion coupled-cluster with single and double excitations (EOM-CCSD) and time-dependent density functional (TDDFT) methods to investigate the landscape of excited state potential energy surfaces across a number of geometric conformations proposed as ICT structures. In order to correlate these geometries and valence excited states in terms of potential experimental observables, we have calculated the nitrogen K-edge ground and excited state absorption spectra for each of the predicted "signpost" structures and identified several key spectral features that could be used to interpret a future time-resolved X-ray absorption experiment.
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Affiliation(s)
- Avdhoot Datar
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Saisrinivas Gudivada
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Devin A Matthews
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
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9
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Kahk JM, Lischner J. Combining the Δ-Self-Consistent-Field and GW Methods for Predicting Core Electron Binding Energies in Periodic Solids. J Chem Theory Comput 2023. [PMID: 37163299 DOI: 10.1021/acs.jctc.3c00121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
For the computational prediction of core electron binding energies in solids, two distinct kinds of modeling strategies have been pursued: the Δ-Self-Consistent-Field method based on density functional theory (DFT), and the GW method. In this study, we examine the formal relationship between these two approaches and establish a link between them. The link arises from the equivalence, in DFT, between the total energy difference result for the first ionization energy, and the eigenvalue of the highest occupied state, in the limit of infinite supercell size. This link allows us to introduce a new formalism, which highlights how in DFT─even if the total energy difference method is used to calculate core electron binding energies─the accuracy of the results still implicitly depends on the accuracy of the eigenvalue at the valence band maximum in insulators, or at the Fermi level in metals. We examine whether incorporating a quasiparticle correction for this eigenvalue from GW theory improves the accuracy of the calculated core electron binding energies, and find that the inclusion of vertex corrections is required for achieving quantitative agreement with experiment.
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Affiliation(s)
- J Matthias Kahk
- Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia
| | - Johannes Lischner
- Department of Physics, Department of Materials, and the Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ, United Kingdom
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10
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Huang M, Evangelista FA. A study of core-excited states of organic molecules computed with the generalized active space driven similarity renormalization group. J Chem Phys 2023; 158:124112. [PMID: 37003756 DOI: 10.1063/5.0137096] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
Abstract
This work examines the accuracy and precision of x-ray absorption spectra computed with a multireference approach that combines generalized active space (GAS) references with the driven similarity renormalization group (DSRG). We employ the x-ray absorption benchmark of organic molecule (XABOOM) set, consisting of 116 transitions from mostly organic molecules [Fransson et al., J. Chem. Theory Comput. 17, 1618 (2021)]. Several approximations to a full-valence active space are examined and benchmarked. Absolute excitation energies and intensities computed with the GAS-DSRG truncated to second-order in perturbation theory are found to systematically underestimate experimental and reference theoretical values. Third-order perturbative corrections significantly improve the accuracy of GAS-DSRG absolute excitation energies, bringing the mean absolute deviation from experimental values down to 0.32 eV. The ozone molecule and glyoxylic acid are particularly challenging for second-order perturbation theory and are examined in detail to assess the importance of active space truncation and intruder states.
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Affiliation(s)
- Meng Huang
- Department of Chemistry and Cherry Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA
| | - Francesco A Evangelista
- Department of Chemistry and Cherry Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA
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11
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Datar A, Wright C, Matthews DA. Theoretical Investigation of the X-ray Stark Effect in Small Molecules. J Phys Chem A 2023; 127:1576-1587. [PMID: 36787229 DOI: 10.1021/acs.jpca.2c08311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
We have studied the Stark effect in the soft x-ray region for various small molecules by calculating the field-dependent x-ray absorption spectra. This effect is explained in terms of the response of molecular orbitals (core and valence), the molecular dipole moment, and the molecular geometry to the applied electric field. A number of consistent trends are observed linking the computed shifts in absorption energies and intensities with specific features of the molecular electronic structure. We find that both the virtual molecular orbitals (valence and/or Rydberg) as well as the core orbitals contribute to observed trends in a complementary fashion. This initial study highlights the potential impact of x-ray Stark spectroscopy as a tool to study electronic structure and environmental perturbations at a submolecular scale.
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Affiliation(s)
- Avdhoot Datar
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Catherine Wright
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Devin A Matthews
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
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12
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Mester D, Kállay M. Double-Hybrid Density Functional Theory for Core Excitations: Theory and Benchmark Calculations. J Chem Theory Comput 2023; 19:1310-1321. [PMID: 36721871 PMCID: PMC9979613 DOI: 10.1021/acs.jctc.2c01222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The double-hybrid (DH) time-dependent density functional theory is extended to core excitations. Two different DH formalisms are presented utilizing the core-valence separation (CVS) approximation. First, a CVS-DH variant is introduced relying on the genuine perturbative second-order correction, while an iterative analogue is also presented using our second-order algebraic-diagrammatic construction [ADC(2)]-based DH ansatz. The performance of the new approaches is tested for the most popular DH functionals using the recently proposed XABOOM [J. Chem. Theory Comput.2021, 17, 1618] benchmark set. In order to make a careful comparison, the accuracy and precision of the methods are also inspected. Our results show that the genuine approaches are highly competitive with the more advanced CVS-ADC(2)-based methods if only excitation energies are required. In contrast, as expected, significant differences are observed in oscillator strengths; however, the precision is acceptable for the genuine functionals as well. Concerning the performance of the CVS-DH approaches, the PBE0-2/CVS-ADC(2) functional is superior, while its spin-opposite-scaled variant is also recommended as a cost-effective alternative. For these approaches, significant improvements are realized in the error measures compared with the popular CVS-ADC(2) method.
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Affiliation(s)
- Dávid Mester
- Department
of Physical Chemistry and Materials Science, Faculty of Chemical Technology
and Biotechnology, Budapest University of
Technology and Economics, Müegyetem rkp. 3, H-1111Budapest, Hungary,ELKH-BME
Quantum Chemistry Research Group, Müegyetem rkp. 3, H-1111Budapest, Hungary,MTA-BME
Lendület Quantum Chemistry Research Group, Müegyetem rkp. 3, H-1111Budapest, Hungary,
| | - Mihály Kállay
- Department
of Physical Chemistry and Materials Science, Faculty of Chemical Technology
and Biotechnology, Budapest University of
Technology and Economics, Müegyetem rkp. 3, H-1111Budapest, Hungary,ELKH-BME
Quantum Chemistry Research Group, Müegyetem rkp. 3, H-1111Budapest, Hungary,MTA-BME
Lendület Quantum Chemistry Research Group, Müegyetem rkp. 3, H-1111Budapest, Hungary,
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13
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Park YC, Perera A, Bartlett RJ. Density functionals for core excitations. J Chem Phys 2022; 157:094107. [PMID: 36075732 DOI: 10.1063/5.0111095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The core excitation energies and related principal ionization energies are obtained for selected molecules using several density functionals and compared with benchmark equation-of-motion coupled cluster (EOM-CC) results. Both time-dependent and time-independent formulations of excitation spectra in the time-dependent density functional theory and the EOM-CC are employed to obtain excited states that are not always easily accessible with the time-independent method. Among those functionals, we find that the QTP(00) functional, which is only parameterized to reproduce the five IPs of water, provides excellent core IPs and core excitation energies, consistently yielding better excitation and ionization energies. We show that orbital eigenvalues of KS density functional theory play an important role in determining the accuracy of the excitation and photoelectron spectra.
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Affiliation(s)
- Young Choon Park
- Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435, USA
| | - Ajith Perera
- Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435, USA
| | - Rodney J Bartlett
- Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435, USA
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14
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Arias-Martinez JE, Cunha LA, Oosterbaan KJ, Lee J, Head-Gordon M. Accurate core excitation and ionization energies from a state-specific coupled-cluster singles and doubles approach. Phys Chem Chem Phys 2022; 24:20728-20741. [PMID: 36004629 DOI: 10.1039/d2cp01998a] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We investigate the use of orbital-optimized references in conjunction with single-reference coupled-cluster theory with single and double substitutions (CCSD) for the study of core excitations and ionizations of 18 small organic molecules, without the use of response theory or equation-of-motion (EOM) formalisms. Three schemes are employed to successfully address the convergence difficulties associated with the coupled-cluster equations, and the spin contamination resulting from the use of a spin symmetry-broken reference, in the case of excitations. In order to gauge the inherent potential of the methods studied, an effort is made to provide reasonable basis set limit estimates for the transition energies. Overall, we find that the two best-performing schemes studied here for ΔCCSD are capable of predicting excitation and ionization energies with errors comparable to experimental accuracies. The proposed ΔCCSD schemes reduces statistical errors against experimental excitation energies by more than a factor of two when compared to the frozen-core core-valence separated (FC-CVS) EOM-CCSD approach - a successful variant of EOM-CCSD tailored towards core excitations.
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Affiliation(s)
- Juan E Arias-Martinez
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA. .,Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Leonardo A Cunha
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA. .,Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Katherine J Oosterbaan
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA.
| | - Joonho Lee
- Department of Chemistry, Columbia University, New York 10027, USA
| | - Martin Head-Gordon
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA. .,Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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15
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Pant R, Ranga S, Bachhar A, Dutta AK. Pair Natural Orbital Equation-of-Motion Coupled-Cluster Method for Core Binding Energies: Theory, Implementation, and Benchmark. J Chem Theory Comput 2022; 18:4660-4673. [PMID: 35786933 DOI: 10.1021/acs.jctc.2c00165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present the theory and implementation of a lower scaling core-valence separated equation-of-motion coupled-cluster approach based on domain-based local pair natural orbitals for core binding energies. The accuracy of the new method has been compared with that of the standard equation-of-motion coupled-cluster method and experimentally measured results. The use of pair natural orbitals significantly reduces the computation cost and can be applied to large molecules.
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Affiliation(s)
- Rakesh Pant
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Santosh Ranga
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Arnab Bachhar
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Achintya Kumar Dutta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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16
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Nascimento DR, Govind N. Computational approaches for XANES, VtC-XES, and RIXS using linear-response time-dependent density functional theory based methods. Phys Chem Chem Phys 2022; 24:14680-14691. [PMID: 35699090 DOI: 10.1039/d2cp01132h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The emergence of state-of-the-art X-ray light sources has paved the way for novel spectroscopies that take advantage of their atomic specificity to shed light on fundamental physical, chemical, and biological processes both in the static and time domains. The success of these experiments hinges on the ability to interpret and predict core-level spectra, which has opened avenues for theory to play a key role. Over the last two decades, linear-response time-dependent density functional theory (LR-TDDFT), despite various theoretical challenges, has become a computationally attractive and versatile framework to study excited-state spectra including X-ray spectroscopies. In this context, we focus our discussion on LR-TDDFT approaches for the computation of X-ray Near-Edge Structure (XANES), Valence-to-Core X-ray Emission (VtC-XES), and Resonant Inelastic X-ray Scattering (RIXS) spectroscopies in molecular systems with an emphasis on Gaussian basis set implementations. We illustrate these approaches with applications and provide a brief outlook of possible new directions.
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Affiliation(s)
- Daniel R Nascimento
- Department of Chemistry, The University of Memphis, Memphis, TN, 38152, USA.
| | - Niranjan Govind
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
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17
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Simons M, Matthews DA. Transition-potential coupled cluster II: optimisation of the core orbital occupation number. Mol Phys 2022. [DOI: 10.1080/00268976.2022.2088421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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18
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Zheng X, Zhang C, Jin Z, Southworth SH, Cheng L. Benchmark relativistic delta-coupled-cluster calculations of K-edge core-ionization energies of third-row elements. Phys Chem Chem Phys 2022; 24:13587-13596. [PMID: 35616685 DOI: 10.1039/d2cp00993e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
A benchmark computational study of K-edge core-ionization energies of third-row elements using relativistic delta-coupled-cluster (ΔCC) methods and a revised core-valence separation (CVS) scheme is reported. High-level relativistic (HLR) corrections beyond the spin-free exact two-component theory in its one-electron variant (SFX2C-1e), including the contributions from two-electron picture-change effects, spin-orbit coupling, the Breit term, and quantum electrodynamics effects, have been taken into account and demonstrated to play an important role. Relativistic ΔCC calculations are shown to provide accurate results for core-ionization energies of third-row elements. The SFX2C-1e-CVS-ΔCC results augmented with HLR corrections show a maximum deviation of less than 0.5 eV with respect to experimental values.
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Affiliation(s)
- Xuechen Zheng
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA.
| | - Chaoqun Zhang
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA.
| | - Zheqi Jin
- Department of Chemistry, University College London, London, WC1E 6BT, UK
| | - Stephen H Southworth
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Lan Cheng
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA.
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19
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Simons M, Matthews DA. Accurate Core-Excited States via Inclusion of Core Triple Excitations in Similarity-Transformed Equation-of-Motion Theory. J Chem Theory Comput 2022; 18:3759-3765. [PMID: 35536592 DOI: 10.1021/acs.jctc.2c00268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The phenomenon of orbital relaxation upon excitation of core electrons is a major problem in the linear-response treatment of core-hole spectroscopies. Rather than addressing relaxation through direct dynamical correlation of the excited state via equation-of-motion coupled cluster theory (EOMEE-CC), we extend the alternative similarity-transformed equation-of-motion coupled cluster theory (STEOMEE-CC) by including the core-valence separation (CVS) and correlation of triple excitations only within the calculation of core ionization energies. This new method, CVS-STEOMEE-CCSD+cT, significantly improves on CVS-EOMEE-CCSD and unmodified CVS-STEOMEE-CCSD when compared to full CVS-EOM-CCSDT for K-edge core-excitation energies of a set of small molecules. The improvement in both absolute and relative (shifted) peak positions is nearly as good as that for transition-potential coupled cluster (TP-CC), which includes an explicit treatment of orbital relaxation, and CVS-EOMEE-CCSD*, which includes a perturbative treatment of triple excitations.
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Affiliation(s)
- Megan Simons
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
| | - Devin A Matthews
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, United States
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20
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Matz F, Jagau TC. Molecular Auger Decay Rates from Complex-Variable Coupled-Cluster Theory. J Chem Phys 2022; 156:114117. [DOI: 10.1063/5.0075646] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The emission of an Auger electron is the predominant relaxation mechanism of core-vacant states in molecules composed of light nuclei. In this non-radiative decay process, one valence electron fills the core vacancy while a second valence electron is emitted into the ionization continuum. Because of this coupling to the continuum, core-vacant states represent electronic resonances that can be tackled with standard quantum-chemical methods only if they are approximated as bound states, meaning that Auger decay is neglected. Here, we present an approach to compute Auger decay rates of core-vacant states from coupled-cluster and equation-of-motion coupled-cluster wave functions combined with complex scaling of the Hamiltonian or, alternatively, complex-scaled basis functions. Through energy decomposition analysis, we illustrate how complex-scaled methods are capable of describing the coupling to the ionization continuum without the need to model the wave function of the Auger electron explicitly. In addition, we introduce in this work several approaches for the determination of partial decay widths and Auger branching ratios from complex-scaled coupled-cluster wave functions. We demonstrate the capabilities of our new approach by computations on core-ionized states of neon, water, dinitrogen, and benzene. Coupled-cluster and equation-of-motion coupled-cluster theory in the singles and doubles approximation both deliver excellent results for total decay widths, whereas we find partial widths more straightforward to evaluate with the former method. We also observe that the requirements towards the basis set are less arduous for Auger decay than for other types of resonances so that extensions to larger molecules are readily possible.
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Affiliation(s)
- Florian Matz
- Katholieke Universiteit Leuven Departement Chemie, Belgium
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21
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Ranga S, Dutta AK. A Core-Valence Separated Similarity Transformed EOM-CCSD Method for Core-Excitation Spectra. J Chem Theory Comput 2021; 17:7428-7446. [PMID: 34814683 DOI: 10.1021/acs.jctc.1c00402] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present the theory and implementation of a core-valence separated similarity transformed EOM-CCSD (STEOM-CCSD) method for K-edge core excitation spectra. The method can select an appropriate active space using CIS natural orbitals and near "black box" to use. The second similarity transformed Hamiltonian is diagonalized in the space of single excitation. Therefore, the final diagonalization step is free from the convergence problem arising due to the coupling of the core-excited states with the continuum of doubly excited states. Convergence trouble can appear for the preceding core-ionized state calculation in STEOM-CCSD. A core-valence separation (CVS) scheme compatible with the natural orbital based active space selection (CVS-STEOM-CCSD-NO) is implemented to overcome the problem. The CVS-STEOM-CCSD-NO has a similar accuracy to that of the standard CVS-EOM-CCSD method but comes with a lower computational cost. The modification required in the CVS scheme to make use of the CIS natural orbital is highlighted. The suitability of the CVS-STEOM-CCSD-NO method for chemical application is demonstrated by simulating the K-edge spectra of glycine and thymine.
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Affiliation(s)
- Santosh Ranga
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Achintya Kumar Dutta
- Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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22
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Halbert L, Vidal ML, Shee A, Coriani S, Severo Pereira Gomes A. Relativistic EOM-CCSD for Core-Excited and Core-Ionized State Energies Based on the Four-Component Dirac-Coulomb(-Gaunt) Hamiltonian. J Chem Theory Comput 2021; 17:3583-3598. [PMID: 33944570 DOI: 10.1021/acs.jctc.0c01203] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We report an implementation of the core-valence separation approach to the four-component relativistic Hamiltonian-based equation-of-motion coupled-cluster with singles and doubles theory (CVS-EOM-CCSD) for the calculation of relativistic core-ionization potentials and core-excitation energies. With this implementation, which is capable of exploiting double group symmetry, we investigate the effects of the different CVS-EOM-CCSD variants and the use of different Hamiltonians based on the exact two-component (X2C) framework on the energies of different core-ionized and -excited states in halogen- (CH3I, HX, and X-, X = Cl-At) and xenon-containing (Xe, XeF2) species. Our results show that the X2C molecular mean-field approach [Sikkema, J.; J. Chem. Phys. 2009, 131, 124116], based on four-component Dirac-Coulomb mean-field calculations (2DCM), is capable of providing core excitations and ionization energies that are nearly indistinguishable from the reference four-component energies for up to and including fifth-row elements. We observe that two-electron integrals over the small-component basis sets lead to non-negligible contributions to core binding energies for the K and L edges for atoms such as iodine or astatine and that the approach based on Dirac-Coulomb-Gaunt mean-field calculations (2DCGM) are significantly more accurate than X2C calculations for which screened two-electron spin-orbit interactions are included via atomic mean-field integrals.
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Affiliation(s)
- Loïc Halbert
- CNRS, UMR 8523-PhLAM-Physique des Lasers, Atomes et Molécules, Université de Lille, F-59000 Lille, France
| | - Marta L Vidal
- DTU Chemistry-Department of Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - Avijit Shee
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Sonia Coriani
- DTU Chemistry-Department of Chemistry, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
| | - André Severo Pereira Gomes
- CNRS, UMR 8523-PhLAM-Physique des Lasers, Atomes et Molécules, Université de Lille, F-59000 Lille, France
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23
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Bilalbegović G, Maksimović A, Valencic LA, Lehtola S. Sulfur Molecules in Space by X-rays: A Computational Study. ACS EARTH & SPACE CHEMISTRY 2021; 5:436-448. [PMID: 33842801 PMCID: PMC8028330 DOI: 10.1021/acsearthspacechem.0c00238] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 02/12/2021] [Accepted: 02/15/2021] [Indexed: 06/12/2023]
Abstract
X-ray astronomy lacks high resolution spectra of interstellar dust analogues and molecules, severely hampering interstellar medium studies based on upcoming X-ray missions. Various theoretical approaches may be used to address this problem, but they must first be shown to reproduce reliable spectra compared to the experiment. In this work, we calculate the sulfur K edge X-ray absorption spectra of H2S, SO2, and OCS, whose spectra are already known from X-ray experiments and predict the X-ray spectrum of CS, which as far as we are aware has not been measured, thereby hampering its detection by X-ray telescopes. We chose these four molecules as the astrochemistry of sulfur is an unsolved problem and as the four molecules are already known to exist in space. We consider three types of methods for modeling the X-ray spectra: more accurate calculations with the algebraic-diagrammatic construction (ADC) and the CC2, CCSD, and CC3 coupled cluster (CC) approaches as well as more affordable ones with transition potential density functional theory (TP-DFT). A comparison of our computational results to previously reported experimental spectra shows that the core-valence separation (CVS) approaches CVS-ADC(2)-x and CVS-CC3 generally yield a good qualitative level of agreement with the experiment, suggesting that they can be used for interpreting measured spectra, while the TP-DFT method is not reliable for these molecules. However, quantitative agreement with the experiment is still outside the reach of the computational methods studied in this work.
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Affiliation(s)
- Goranka Bilalbegović
- Department
of Physics, Faculty of Science, University
of Zagreb, Bijenička
cesta 32, 10000 Zagreb, Croatia
| | - Aleksandar Maksimović
- Center
of Excellence for Advanced Materials and Sensing Devices, Rudjer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| | - Lynne A. Valencic
- NASA
Goddard Space Flight Center, Greenbelt, 20771 Maryland, United States
- Department
of Physics & Astronomy, The Johns Hopkins
University, 366 Bloomberg
Center, 3400 N. Charles Street, Baltimore, 21218 Maryland, United States
| | - Susi Lehtola
- Department
of Chemistry, University of Helsinki, P.O. Box 55, A. I. Virtasen aukio
1, FI-00014 Helsinki, Finland
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24
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Fransson T, Brumboiu IE, Vidal ML, Norman P, Coriani S, Dreuw A. XABOOM: An X-ray Absorption Benchmark of Organic Molecules Based on Carbon, Nitrogen, and Oxygen 1s → π* Transitions. J Chem Theory Comput 2021; 17:1618-1637. [PMID: 33544612 PMCID: PMC8023667 DOI: 10.1021/acs.jctc.0c01082] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Indexed: 01/05/2023]
Abstract
The performance of several standard and popular approaches for calculating X-ray absorption spectra at the carbon, nitrogen, and oxygen K-edges of 40 primarily organic molecules up to the size of guanine has been evaluated, focusing on the low-energy and intense 1s → π* transitions. Using results obtained with CVS-ADC(2)-x and fc-CVS-EOM-CCSD as benchmark references, we investigate the performance of CC2, ADC(2), ADC(3/2), and commonly adopted density functional theory (DFT)-based approaches. Here, focus is on precision rather than on accuracy of transition energies and intensities-in other words, we target relative energies and intensities and the spread thereof, rather than absolute values. The use of exchange-correlation functionals tailored for time-dependent DFT calculations of core excitations leads to error spreads similar to those seen for more standard functionals, despite yielding superior absolute energies. Long-range corrected functionals are shown to perform particularly well compared to our reference data, showing error spreads in energy and intensity of 0.2-0.3 eV and ∼10%, respectively, as compared to 0.3-0.6 eV and ∼20% for a typical pure hybrid. In comparing intensities, state mixing can complicate matters, and techniques to avoid this issue are discussed. Furthermore, the influence of basis sets in high-level ab initio calculations is investigated, showing that reasonably accurate results are obtained with the use of 6-311++G**. We name this benchmark suite as XABOOM (X-ray absorption benchmark of organic molecules) and provide molecular structures and ground-state self-consistent field energies and spectroscopic data. We believe that it provides a good assessment of electronic structure theory methods for calculating X-ray absorption spectra and will become useful for future developments in this field.
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Affiliation(s)
- Thomas Fransson
- Interdisciplinary
Center for Scientific Computing, Ruprecht-Karls
University, Im Neuenheimer
Feld 205, 69120 Heidelberg, Germany
- Fysikum, Stockholm University, Albanova, 10691 Stockholm, Sweden
| | - Iulia E. Brumboiu
- Department
of Theoretical Chemistry and Biology, KTH
Royal Institute of Technology, 10691 Stockholm, Sweden
- Department
of Chemistry, Korea Advanced Institute of
Science and Technology, 34141 Daejeon, Korea
| | - Marta L. Vidal
- DTU
Chemistry, Technical University of Denmark, Kemitorvet Bldg 207, DK-2800 Kongens Lyngby, Denmark
| | - Patrick Norman
- Department
of Theoretical Chemistry and Biology, KTH
Royal Institute of Technology, 10691 Stockholm, Sweden
| | - Sonia Coriani
- DTU
Chemistry, Technical University of Denmark, Kemitorvet Bldg 207, DK-2800 Kongens Lyngby, Denmark
- Department
of Chemistry, NTNU-Norwegian University
of Science and Technology, N-7991 Trondheim, Norway
| | - Andreas Dreuw
- Interdisciplinary
Center for Scientific Computing, Ruprecht-Karls
University, Im Neuenheimer
Feld 205, 69120 Heidelberg, Germany
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25
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Tsuru S, Vidal ML, Pápai M, Krylov AI, Møller KB, Coriani S. An assessment of different electronic structure approaches for modeling time-resolved x-ray absorption spectroscopy. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:024101. [PMID: 33786337 PMCID: PMC7986275 DOI: 10.1063/4.0000070] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 02/11/2021] [Indexed: 05/06/2023]
Abstract
We assess the performance of different protocols for simulating excited-state x-ray absorption spectra. We consider three different protocols based on equation-of-motion coupled-cluster singles and doubles, two of them combined with the maximum overlap method. The three protocols differ in the choice of a reference configuration used to compute target states. Maximum-overlap-method time-dependent density functional theory is also considered. The performance of the different approaches is illustrated using uracil, thymine, and acetylacetone as benchmark systems. The results provide guidance for selecting an electronic structure method for modeling time-resolved x-ray absorption spectroscopy.
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Affiliation(s)
- Shota Tsuru
- DTU Chemistry, Technical University of Denmark, Kemitorvet Building 207, DK-2800 Kgs. Lyngby, Denmark
| | - Marta L. Vidal
- DTU Chemistry, Technical University of Denmark, Kemitorvet Building 207, DK-2800 Kgs. Lyngby, Denmark
| | - Mátyás Pápai
- DTU Chemistry, Technical University of Denmark, Kemitorvet Building 207, DK-2800 Kgs. Lyngby, Denmark
| | - Anna I. Krylov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Klaus B. Møller
- DTU Chemistry, Technical University of Denmark, Kemitorvet Building 207, DK-2800 Kgs. Lyngby, Denmark
| | - Sonia Coriani
- DTU Chemistry, Technical University of Denmark, Kemitorvet Building 207, DK-2800 Kgs. Lyngby, Denmark
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26
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Abstract
We present a new and efficient implementation of the closed shell coupled cluster singles and doubles with perturbative triples method (CC3) in the electronic structure program eT. Asymptotically, a ground state calculation has an iterative cost of 4nV4nO3 floating point operations (FLOP), where nV and nO are the number of virtual and occupied orbitals, respectively. The Jacobian and transpose Jacobian transformations, required to iteratively solve for excitation energies and transition moments, both require 8nV4nO3 FLOP. We have also implemented equation of motion (EOM) transition moments for CC3. The EOM transition densities require recalculation of triples amplitudes, as nV3nO3 tensors are not stored in memory. This results in a noniterative computational cost of 10nV4nO3 FLOP for the ground state density and 26nV4nO3 FLOP per state for the transition densities. The code is compared to the CC3 implementations in CFOUR, DALTON, and PSI4. We demonstrate the capabilities of our implementation by calculating valence and core excited states of l-proline.
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Affiliation(s)
- Alexander
C. Paul
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
| | - Rolf H. Myhre
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
| | - Henrik Koch
- Department
of Chemistry, Norwegian University of Science
and Technology, NTNU, 7491 Trondheim, Norway
- Scuola
Normale Superiore, Piazza dei Cavaleri 7, 56126 Pisa, Italy
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27
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Abstract
The problem of orbital relaxation in computational core-hole spectroscopies, including x-ray absorption and x-ray photoionization, has long plagued linear response approaches, including equation-of-motion coupled cluster with singles and doubles (EOM-CCSD). Instead of addressing this problem by including additional electron correlation, we propose an explicit treatment of orbital relaxation via the use of "transition potential" reference orbitals, leading to a transition-potential coupled cluster (TP-CC) family of methods. One member of this family, in particular, TP-CCSD(12), is found to essentially eliminate the orbital relaxation error and achieve the same level of accuracy for the core-hole spectra as is typically expected of EOM-CCSD in the valence region. These results show that very accurate x-ray absorption spectra for molecules with first-row atoms can be computed at a cost essentially the same as that for EOM-CCSD.
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Affiliation(s)
- Megan Simons
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, USA
| | - Devin A Matthews
- Department of Chemistry, Southern Methodist University, Dallas, Texas 75275, USA
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28
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Garner SM, Neuscamman E. Core excitations with excited state mean field and perturbation theory. J Chem Phys 2020; 153:154102. [PMID: 33092351 DOI: 10.1063/5.0020595] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
We test the efficacy of excited state mean field theory and its excited-state-specific perturbation theory on the prediction of K-edge positions and x-ray peak separations. We find that the mean field theory is surprisingly accurate, even though it contains no accounting of differential electron correlation effects. In the perturbation theory, we test multiple core-valence separation schemes and find that, with the mean field theory already so accurate, electron-counting biases in one popular separation scheme become a dominant error when predicting K-edges. Happily, these appear to be relatively easy to correct for, leading to a perturbation theory for K-edge positions that is lower scaling and more accurate than coupled cluster theory and competitive in accuracy with recent high-accuracy results from restricted open-shell Kohn-Sham theory. For peak separations, our preliminary data show excited state mean field theory to be exceptionally accurate, but more extensive testing will be needed to see how it and its perturbation theory compare to coupled cluster peak separations more broadly.
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Affiliation(s)
- Scott M Garner
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Eric Neuscamman
- Department of Chemistry, University of California, Berkeley, California 94720, USA
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