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A Fock space coupled cluster based probing of the single- and double-ionization profiles for the poly-cyclic aromatic hydrocarbons and conjugated polyenes. J Chem Phys 2021; 154:114106. [PMID: 33752359 DOI: 10.1063/5.0037557] [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
Sequential formation of a poly-cyclic aromatic hydrocarbon (PAH) dication in the H I regions of the interstellar medium (ISM) is proposed to be a function of internal energy of the doubly ionized PAHs, which, in turn, is dependent on the single- and double-ionization potentials of the system. This sets a limit on the single- and double-ionization energies of the system(s) that can further undergo sequential absorption of two photons, leading to a dication (PAH+2). Here, we report the single-ionization (I+1) and double-ionization (I+2) energies and the I+2/I+1 ratio for some selected PAHs and conjugated polyenes obtained using the Fock space coupled cluster technique, enabling simultaneous consideration of several electronic states of different characters. The I+2 to I+1 ratio bears a constant ratio, giving allowance to determine I+2 from the knowledge of single-ionization (I+1) and vice versa. Our observations are in good agreement with the established literature findings, confirming the reliability of our estimates. The measured single- and double-ionization energies further demonstrate that the sequential formation and fragmentation of a PAH dication in the H I regions of the ISM for systems such as benzene and conjugated polyenes such as ethylene and butadiene are quite unlikely because I+2-I+1 for such system(s) is higher than the available photon energy in the H I regions of the ISM. Present findings may be useful to understand the formation and underlying decay mechanisms of multiply charged ions from PAHs and related compounds that may accentuate the exploration of the phenomenon of high-temperature superconductivity.
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Description of the Methylene Amidogene Radical and Its Anion with an Economical Treatment of Correlation Effects Using Density Functional Theory Orbitals. J Phys Chem A 2021; 125:543-558. [PMID: 33417452 DOI: 10.1021/acs.jpca.0c08635] [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
The ground and low-lying excited state electronic structural properties (such as equilibrium geometries, harmonic frequencies, excitation energies, barrier energy, and so on) of the methylene amidogene radical (H2CN) and its anion (H2CN-) have been studied using the CASCI (complete active space configuration interaction) and SSMRPT (state-specific multireference Møller-Plesset perturbation theory) methods with density function theory (DFT) orbitals. Here, the span of the active orbitals have been obtained from Kohn-Sham DFT using B3LYP exchange-correlation functionals in the CASCI (DFT-CASCI) approximation to describe nondynamic correlation associated with electronic degeneracies. The DFT-SSMRPT protocol provides an attractive way to deal with both dynamical and nondynamical correlation effects in strongly correlated systems such as H2CN and H2CN-. The present work clearly indicates that the electronic absorption band near 35,050 cm-1 corresponds to the B̃2A1 ← X̃2B2 transition. DFT-SSMRPT findings are in close agreement with high-level theoretical estimates. It is concluded that the transition at 1725 cm-1 could be due to the CN stretching of the trans-HCNH isomer which is originally assigned to the CN stretch of H2CN in the experiment. The present results confirm most of the previous vibrational assignments. It is not possible to definitively assign a transition to the 35,600 cm-1 band with the present estimations, suggesting further experiment is urgently called for.
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Taming the excited states of butadiene, hexatriene, and octatetraene using state specific multireference perturbation theory with density functional theory orbitals. J Chem Phys 2020; 152:244105. [DOI: 10.1063/5.0007198] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Acetyl zingerone: An efficacious multifunctional ingredient for continued protection against ongoing DNA damage in melanocytes after sun exposure ends. Int J Cosmet Sci 2019; 42:36-45. [PMID: 31538664 PMCID: PMC7004018 DOI: 10.1111/ics.12582] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 09/06/2019] [Accepted: 09/16/2019] [Indexed: 11/26/2022]
Abstract
Objective Recent research has shown that significant levels of cyclobutane pyrimidine dimers (CPDs) in DNA continue to form in melanocytes for several hours in the dark after exposure to ultraviolet radiation (UVR) ends. We document the utility of a new multifunctional ingredient, 3‐(4‐hydroxy, 3‐methoxybenzyl)‐pentane‐2,4‐dione (INCI acetyl zingerone (AZ)), to protect melanocytes against CPD formation after UVR exposure ends. Methods The use of AZ as an intervention to reduce CPD formation after irradiation was assessed in vitro by comparing kinetic profiles of CPD formation for several hours after irradiation in cells that were untreated or treated with AZ immediately after irradiation. Multifunctional performance of AZ as an antioxidant, quencher and scavenger was established using industry‐standard in vitro chemical assays, and then, its efficacy in a more biological assay was confirmed by its in vitro ability to reduce intracellular levels of reactive oxygen species (ROS) in keratinocytes exposed to UVA radiation. Molecular photostability was assessed in solution during exposure to solar‐simulated UVR and compared with the conventional antioxidant α‐tocopherol. Results Even when added immediately after irradiation, AZ significantly inhibited ongoing formation of CPDs in melanocytes after exposure to UVA. Incubation with AZ before irradiation decreased intracellular levels of UVA‐induced ROS formation in keratinocytes. Compared with α‐tocopherol, the molecular structure of AZ endows it with significantly better photostability and efficacy to neutralize free radicals (∙OH, ∙OOH), physically quench singlet oxygen (1O2) and scavenge peroxynitrite (ONOO−). Conclusion These results designate AZ as a new type of multifunctional ingredient with strong potential to extend photoprotection of traditional sunscreens and daily skincare products over the first few hours after sun exposure ends.
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Fock-space multireference coupled cluster calculations of Auger energies of noble gas elements using relativistic spinors. J Chem Phys 2019; 151:074114. [DOI: 10.1063/1.5094829] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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A simplified account of the correlation effects to bond breaking processes: The Brillouin-Wigner perturbation theory using a multireference formulation. J Chem Phys 2019. [DOI: 10.1063/1.5097657] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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A confinement induced spectroscopic study of noble gas atoms using equation of motion architecture: Encapsulation within fullerene's voids. J Chem Phys 2018; 147:034111. [PMID: 28734307 DOI: 10.1063/1.4994569] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A relativistic study of spectroscopic properties of the endohedral fullerenes Ng@C60q (where Ng = He, Ne and q=0,±1,±2 are the charges) associated with the C60 molecule has been done using the equation of motion coupled cluster (EOM-CC) methodology. Specific properties estimated are the transition energies, dipole oscillator strengths, and transition probabilities for the low-lying excitations 1s2(1S0) → 1snp (1P1) (n = 2, 3, 4) for He@C60q and 1s22s22p6 (1S0) → 1s22s22p5ns∕nd (1P1) (n = 3, 4) for Ne@C60q, which have been compared with those for the isolated atom to depict the confinement effect of the host molecule on the encapsulated atom. This is accomplished by introducing an effective potential to the atomic Hamiltonian induced by the fullerene moiety and its charge. The EOM-CC results have been compared with those estimated with the random phase approximation (and configuration interaction singles) to understand the effect of electron correlation under such confinement. The systematic and interesting behavior of the properties is highlighted indicating the effect of fullerene cage potential on the redistribution of electron density of the guest atom.
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Improvement of hydration and epidermal barrier function in human skin by a novel compound isosorbide dicaprylate. Int J Cosmet Sci 2017; 39:518-526. [PMID: 28543784 DOI: 10.1111/ics.12405] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2017] [Accepted: 05/20/2017] [Indexed: 11/29/2022]
Abstract
OBJECTIVE The study involved the synthesis of a novel derivative of caprylic acid - isosorbide dicaprylate (IDC) - and the evaluation of its potential in improving water homoeostasis and epidermal barrier function in human skin. METHODS The effect of IDC on gene expression was assayed in skin organotypic cultures by DNA microarrays. The results were then confirmed for a few key genes by quantitative PCR, immuno- and cytochemistry. Final validation of skin hydration properties was obtained by four separate clinical studies. Level of hydration was measured by corneometer either by using 2% IDC lotion alone vs placebo or in combination with 2% glycerol lotion vs 2% glycerol only. A direct comparison in skin hydration between 2% IDC and 2% glycerol lotions was also carried out. The epidermal barrier function improvement was assessed by determining changes in transepidermal water loss (TEWL) on the arms before and after treatment with 2% IDC lotion versus placebo. RESULTS IDC was found to upregulate the expression of AQP3, CD44 and proteins involved in keratinocyte differentiation as well as the formation and function of stratum corneum. A direct comparison between 2% IDC versus 2% glycerol lotions revealed a three-fold advantage of IDC in providing skin hydration. Severely dry skin treated with 2% IDC in combination with 2% glycerol showed 133% improvement, whereas 35% improvement was observed with moderately dry human skin. CONCLUSION Topical isosorbide dicaprylate favourably modulates genes involved in the maintenance of skin structure and function, resulting in superior clinical outcomes. By improving skin hydration and epidermal permeability barrier, it offers therapeutic applications in skin ageing.
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Description of C2 dissociation using a naive treatment of dynamical correlation in the presence of quasidegeneracy of varying degree. Mol Phys 2017. [DOI: 10.1080/00268976.2017.1323129] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Four-Component Relativistic State-Specific Multireference Perturbation Theory with a Simplified Treatment of Static Correlation. J Phys Chem A 2017; 121:1487-1501. [PMID: 28112937 DOI: 10.1021/acs.jpca.6b11348] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The relativistic multireference (MR) perturbative approach is one of the most successful tools for the description of computationally demanding molecular systems of heavy elements. We present here the ground state dissociation energy surfaces, equilibrium bond lengths, harmonic frequencies, and dissociation energies of Ag2, Cu2, Au2, and I2 computed using the four-component (4c) relativistic spinors based state-specific MR perturbation theory (SSMRPT) with improved virtual orbital complete active space configuration interaction (IVO-CASCI) functions. The IVO-CASCI method is a simple, robust, useful and lower cost alternative to the complete active space self-consistent field approach for treating quasidegenerate situations. The redeeming features of the resulting method, termed as 4c-IVO-SSMRPT, lies in (i) manifestly size-extensivity, (ii) exemption from intruder problems, (iii) the freedom of convenient multipartitionings of the Hamiltonian, (iv) flexibility of the relaxed and unrelaxed descriptions of the reference coefficients, and (v) manageable cost/accuracy ratio. The present method delivers accurate descriptions of dissociation processes of heavy element systems. Close agreement with reference values has been found for the calculated molecular constants indicating that our 4c-IVOSSMRPT provides a robust and economic protocol for determining the structural properties for the ground state of heavy element molecules with eloquent MR character as it treats correlation and relativity on equal footing.
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Improved virtual orbitals in state specific multireference perturbation theory for prototypes of quasidegenerate electronic structure. J Chem Phys 2017; 146:064111. [DOI: 10.1063/1.4975322] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Communication: Viewing the ground and excited electronic structures of platinum and its ion through the window of relativistic coupled cluster method. J Chem Phys 2017; 146:011102. [DOI: 10.1063/1.4973706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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A simplified ab initio treatment of diradicaloid structures produced from stretching and breaking chemical bonds. Phys Chem Chem Phys 2017; 19:22282-22301. [DOI: 10.1039/c7cp03564k] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
With a proper choice of active spaces, the single root perturbation theory employing improved virtual orbitals can flawlessly describe the ground, excited, ionized, and dissociated states having varying degrees of degeneracy at the expense of low computational cost.
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Relativistic state-specific multireference coupled cluster theory description for bond-breaking energy surfaces. J Chem Phys 2016; 145:124303. [DOI: 10.1063/1.4962911] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Taming the Electronic Structure of Diradicals through the Window of Computationally Cost Effective Multireference Perturbation Theory. J Phys Chem A 2016; 120:5897-916. [DOI: 10.1021/acs.jpca.6b03211] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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State-specific multireference perturbation theory: development and present status. WILEY INTERDISCIPLINARY REVIEWS-COMPUTATIONAL MOLECULAR SCIENCE 2016. [DOI: 10.1002/wcms.1248] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Relativistic state-specific multireference perturbation theory incorporating improved virtual orbitals: Application to the ground state single-bond dissociation. J Comput Chem 2015; 36:1954-72. [PMID: 26272333 DOI: 10.1002/jcc.24037] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Revised: 07/01/2015] [Accepted: 07/02/2015] [Indexed: 11/07/2022]
Abstract
Using four-component (4c) relativistic spinors, we present a computationally economical relativistic ab initio method for molecular systems employing our recently proposed second-order state-specific multireference perturbation theory (SSMRPT) incorporating the improved virtual orbital-complete active space configuration interaction (IVO-CASCI) reference wavefunction. The resulting method, 4c-IVO-SSMRPT [calculate one state at a time] is tested in pilot calculations on the homonuclear dimers including Li(2), Na(2), K(2), Rb(2), F(2), Cl(2), and Br(2) through the computations of the ground state potential energy curves (PECs). As SSMRPT curbs intruder effects, 4c-IVO-SSMRPT is numerically stable. To our knowledge, the SSMRPT in the 4c relativistic framework has not been explored in the past. Selective spectroscopic constants that are closely related to the correct shape and accuracy of the energy surfaces have been extracted from the computed PECs. For the halogen molecules, a relativistic destabilization of the bond has been found. Relativistic and electron correlation effects need to be incorporated to get reliable estimates. Our results are in good accordance with reference theoretical and experimental data which manifests the computational accuracy and efficiency of the new 4c-IVO-SSMRPT method. The method opens for an improved description of MR systems containing heavy elements. The inexpensiveness of IVO-CASCI makes 4c-IVO-SSMRPT method promising for studies on large systems of heavy elements.
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State-specific multireference perturbation theory with improved virtual orbitals: Taming the ground state of F2, Be2,and N2. J Comput Chem 2015; 36:907-25. [DOI: 10.1002/jcc.23873] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 01/09/2015] [Accepted: 01/11/2015] [Indexed: 11/07/2022]
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Profiling the binding motif between Be and Mg in the ground state via a single-reference coupled cluster method. Mol Phys 2015. [DOI: 10.1080/00268976.2014.996616] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Revisiting the ‘cis-effect’ in 1,2-difluoro derivatives of ethylene and diazene usingab initiomultireference methods. Mol Phys 2014. [DOI: 10.1080/00268976.2014.938710] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Reappraisal of nuclear quadrupole moments of atomic halogens via relativistic coupled cluster linear response theory for the ionization process. J Phys Chem A 2013; 117:12616-27. [PMID: 24171543 DOI: 10.1021/jp408645g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The coupled cluster based linear response theory (CCLRT) with four-component relativistic spinors is employed to compute the electric field gradients (EFG) of (35)Cl, (79)Br, and (127)I nuclei. The EFGs resulting from these calculations are combined with experimental nuclear quadrupole coupling constants (NQCC) to determine the nuclear quadrupole moments (NQM), Q of the halide nuclei. Our estimated NQMs [(35)Cl = -81.12 mb, (79)Br = 307.98 mb, and (127)I = -688.22 mb] agree well with the new atomic values [(35)Cl = -81.1(1.2), (79)Br = 302(5), and (127)I = -680(10) mb] obtained via Fock space multireference coupled cluster method with the Dirac-Coulomb-Breit Hamiltonian. Although our estimated Q((79)Br) value deviates from the accepted reference value of 313(3) mb, it agrees well with the recently recommended value, Q((79)Br) = 308.7(20) mb. Good agreement with current reference data indicates the accuracy of the proposed value for these halogen nuclei and lends credence to the results obtained via CCLRT approach. The electron affinities yielded by this method with no extra cost are also in good agreement with experimental values, which bolster our belief that the NQMs values for halogen nuclei derived here are reliable.
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Taming the Electronic Structure of Lead and Eka-lead (Flerovium) by the Relativistic Coupled Cluster Method. J Phys Chem A 2013; 117:8555-67. [DOI: 10.1021/jp402376b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Theoretical Studies of the Ground and Excited State Structures of Stilbene. J Phys Chem A 2013; 117:9424-34. [DOI: 10.1021/jp311493w] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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Application of an efficient multireference approach to free-base porphin and metalloporphyrins: Ground, excited, and positive ion states. J Chem Phys 2011; 135:084118. [DOI: 10.1063/1.3627153] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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Ab Initio Multireference Investigation of Disjoint Diradicals: Singlet versus Triplet Ground States. Chemphyschem 2011; 12:2791-7. [DOI: 10.1002/cphc.201100430] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2011] [Indexed: 11/12/2022]
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Prediction of electronic structure of organic radicaloid anions using efficient, economical multireference gradient approach. Phys Chem Chem Phys 2011; 13:7514-23. [PMID: 21423953 DOI: 10.1039/c0cp02106g] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method enables an economical and reasonably accurate treatment of static correlation in systems with significant multireference character, even when using a moderate basis set. This IVO-CASCI method supplants the computationally more demanding complete active space self-consistent field (CASSCF) method by producing comparable accuracy with diminished computational effort because the IVO-CASCI approach does not require additional iterations beyond an initial SCF calculation, nor does it encounter convergence difficulties or multiple solutions that may be found in CASSCF calculations. Our IVO-CASCI analytical gradient approach is applied to compute the equilibrium geometry for the ground and lowest excited state(s) of the theoretically very challenging 2,6-pyridyne, 1,2,3-tridehydrobenzene and 1,3,5-tridehydrobenzene anionic systems for which experiments are lacking, accurate quantum calculations are almost completely absent, and commonly used calculations based on single reference configurations fail to provide reasonable results. Hence, the computational complexity provides an excellent test for the efficacy of multireference methods. The present work clearly illustrates that the IVO-CASCI analytical gradient method provides a good description of the complicated electronic quasi-degeneracies during the geometry optimization process for the radicaloid anions. The IVO-CASCI treatment produces almost identical geometries as the CASSCF calculations (performed for this study) at a fraction of the computational labor. Adiabatic energy gaps to low lying excited states likewise emerge from the IVO-CASCI and CASSCF methods as very similar. We also provide harmonic vibrational frequencies to demonstrate the stability of the computed geometries.
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Second-order state-specific multireference Møller Plesset perturbation theory: Application to energy surfaces of diimide, ethylene, butadiene, and cyclobutadiene. J Comput Chem 2010; 32:325-37. [DOI: 10.1002/jcc.21624] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Geometry Optimization of Radicaloid Systems Using Improved Virtual Orbital-Complete Active Space Configuration Interaction (IVO-CASCI) Analytical Gradient Method. J Phys Chem A 2010; 115:3665-78. [DOI: 10.1021/jp103536w] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Study of equilibrium geometries of diradicaloid systems via state specific multireference Møller–Plesset perturbation theory (SS-MRMPPT). Chem Phys Lett 2010. [DOI: 10.1016/j.cplett.2010.02.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Study of the Ground State Dissociation of Diatomic Molecular Systems Using State-Specific Multireference Perturbation Theory: A Brillouin−Wigner Scheme. J Chem Theory Comput 2010; 6:662-82. [DOI: 10.1021/ct900452n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Second-Order State-Specific Multireference Møller−Plesset Perturbation Theory (SS-MRMPPT) Applied to Geometry Optimization. J Phys Chem A 2010; 114:3668-82. [DOI: 10.1021/jp911581f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Molecular applications of analytical gradient approach for the improved virtual orbital-complete active space configuration interaction method. J Chem Phys 2010; 132:034105. [DOI: 10.1063/1.3290203] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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Investigation of Low-Lying States of Oxygen Molecule via Second-Order Multireference Perturbation Theory: A State-Specific Approach. J Phys Chem A 2009; 113:5972-84. [DOI: 10.1021/jp810910n] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Application of state-specific multireference Møller–Plesset perturbation theory to nonsinglet states. J Chem Phys 2009; 130:014101. [DOI: 10.1063/1.3043364] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
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Application of improved virtual orbital based multireference methods to N2, LiF, and C4H6 systems. J Chem Phys 2008; 129:244108. [DOI: 10.1063/1.3046454] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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Reappraisal ofciseffect in 1,2-dihaloethenes: An improved virtual orbital multireference approach. J Chem Phys 2008; 129:064101. [DOI: 10.1063/1.2958284] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
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Improved virtual orbital multireference Møller–Plesset study of the ground and excited electronic states of protonated acetylene, C2H3+. J Chem Phys 2008; 129:054308. [DOI: 10.1063/1.2958282] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
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Molecular applications of state-specific multireference perturbation theory to HF, H2O, H2S, C2, and N2 molecules. J Chem Phys 2008; 129:024108. [DOI: 10.1063/1.2952666] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Potential energy curve for isomerization of N2H2 and C2H4 using the improved virtual orbital multireference Møller–Plesset perturbation theory. J Chem Phys 2008; 128:144304. [DOI: 10.1063/1.2837662] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Theoretical Study on the Electronic States of Formylcarbene (HC·CHO) and Triplet Ketene (H2 CCO) and the Ultraviolet Absorption Spectra Attributable to These Molecules. J Phys Chem A 2008; 112:4399-404. [DOI: 10.1021/jp712172d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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Effects of partial triple excitations in atomic coupled cluster calculations. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.05.052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Theoretical Study on the Ground and Excited States of Dicyanocarbene (C3N2) and Its Isomers: A Low-Temperature Matrix Emission Spectrum Attributable to 3-Cyano-2H-azirenylidene. J Phys Chem A 2007; 111:4849-54. [PMID: 17497833 DOI: 10.1021/jp066358k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ab initio calculations are used to characterize the ground and low lying excited electronic states of selected dicyanocarbene (C(3)N(2) or C(CN)2) isomers. Our calculated ground state geometries and the corresponding vibrational frequencies agree well with available experimental and theoretical data, thereby providing the reliability of the predicted quantities. The present calculations are used to identify the possible emitting species for some unidentified emission bands observed in certain low-temperature matrices. It is found that the 1(3)A' --> X(1)A' transition of 3-cyano-2H-azirenylidene, that is, cyclic C(2)N-CN (Figure 1c) satisfactorily explains all of the observed spectral features of these bands.
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Geometry optimization using improved virtual orbitals: A complete active space numerical gradient approach. J Chem Phys 2007; 126:114103. [PMID: 17381192 DOI: 10.1063/1.2566692] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The improved virtual orbital-complete active space configuration interaction (IVO-CASCI) method is extended to enable geometry optimization and the calculation of vibrational frequencies for ground and excited states using numerical energy gradients. Applications consider the ground state geometries and vibrational frequencies of the Be2, LiF, H2S, and HCN molecules, as well as excited state properties for HCN, systems that are sufficiently complex to access the efficacy of the method. Comparisons with other standard approaches (self-consistent field, second order Moller-Plesset perturbation theory, complete active space self-consistent field, and coupled cluster singles and doubles methods) demonstrate that the numerical gradient version of the IVO-CASCI approach generally fares comparable to or better for all systems studied. The accurate estimates for the Be2 bond length and vibrational frequency are notable since many other computationally facile methods produce poor results.
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Abstract
In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 angstroms. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 3-A' <-- 1 3-A' of HCN.
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Relativistic coupled-cluster calculations of parity nonconservation in Ba+ by the sum-over-states approach. J Chem Phys 2007; 126:014301. [PMID: 17212492 DOI: 10.1063/1.2404664] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The authors present the results of their calculation for the parity nonconserving 5p(6)6s(1/2)-->5p(6)5d(3/2) transition in Ba+ using the relativistic coupled-cluster theory in the singles, doubles, and partial triples approximation. The contributions from the leading intermediate states are explicitly considered. It is found that the largest contribution comes from the |5p(6)6p(1/2)> state. Their results are in reasonable agreement with other calculations.
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Electric quadrupole moments of the D states of alkaline-earth-metal ions. PHYSICAL REVIEW LETTERS 2006; 96:193001. [PMID: 16803101 DOI: 10.1103/physrevlett.96.193001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Indexed: 05/10/2023]
Abstract
The electric quadrupole moment for the 4d(2)D(5/2) state of (88)Sr(+); one of the most important candidates for an optical clock, has been calculated using the relativistic coupled-cluster theory. This is the first application of this theory to determine atomic electric quadrupole moments. The result of the calculation is presented and the important many-body contributions are highlighted. The calculated electric quadrupole moment is (2.94 +/- 0.07)ea(2)(0), where a(o) is the Bohr radius and the electronic charge while the measured value is (2.6 +/- 0.3) ea(2)(0). This is so far the most accurate determination of the electric quadrupole moment for the above mentioned state. We have also calculated the electric quadrupole moments for the metastable 4d(2)D(3/2) state of 88(Sr(+) and for the 3d(2)D(3/2.5/2) and 5d(2)D(3/2.5/2) states of (43)Ca(+) and (138)Ba(+), respectively.
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Relativistic effective valence shell Hamiltonian method: Excitation and ionization energies of heavy metal atoms. J Chem Phys 2005; 122:204111. [PMID: 15945717 DOI: 10.1063/1.1906206] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The relativistic effective valence shell Hamiltonian H(v) method (through second order) is applied to the computation of the low lying excited and ion states of closed shell heavy metal atoms/ions. The resulting excitation and ionization energies are in favorable agreement with experimental data and with other theoretical calculations. The nuclear magnetic hyperfine constants A and lifetimes tau of excited states are evaluated and they are also in accord with experiment. Some of the calculated quantities have not previously been computed.
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Generation of potential energy curves for the XΣg+1, BΔg+1, and B′Σg+1 states of C2 using the effective valence shell Hamiltonian method. J Chem Phys 2005; 122:154310. [PMID: 15945638 DOI: 10.1063/1.1879812] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Calculations of the ground and excited state potential energy curves of C2 using the third-order effective valence Hamiltonian (Hv3rd) method are benchmarked against full configuration interaction and other correlated single-reference perturbative and nonperturbative theories. The large nonparallelity errors (NPEs) exhibited even by state-of-art coupled cluster calculations through perturbative triples indicate a serious deficiency of these single-reference theories. The Hv method, on the other hand, produces a much reduced NPE, rendering it a viable approximate many-body method for accurately determining global ground and excited state potential energy curvessurfaces.
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Abstract
Tests have been made to benchmark and assess the relative accuracies of low-order multireference perturbation theories as compared to coupled cluster (CC) and full configuration interaction (FCI) methods. Test calculations include the ground and some excited states of the Be, H(2), BeH(2), CH(2), and SiH(2) systems. Comparisons with FCI and CC calculations show that in most cases the effective valence shell Hamiltonian (H(v)) method is more accurate than other low-order multireference perturbation theories, although none of the perturbative methods is as accurate as the CC approximations. We also briefly discuss some of the basic differences among the multireference perturbation theories considered in this work.
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