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Das S, Samanta K. Recent Advances in the Study of Negative-Ion Resonances Using Multiconfigurational Propagator and a Complex Absorbing Potential. Chemphyschem 2023; 24:e202200546. [PMID: 36223261 DOI: 10.1002/cphc.202200546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Revised: 10/12/2022] [Indexed: 02/03/2023]
Abstract
The transient resonances are a challenge to bound state quantum mechanics. These states lie in the continuum part of the spectrum of the Hamiltonian. For this, one has to treat a continuum problem due to electron-molecule scattering and the many-electron correlation problem simultaneously. Moreover, the description of a resonance requires a wavefunction that bridges the part that resembles a bound state with another that resembles a continuum state such that the continuity of the wavefunction and its first derivative with respect to the distance between the incoming projectile and the target is maintained. A review of the recent advances in the theoretical investigation of the negative-ion resonances (NIR) is presented. The NIRs are ubiquitous in nature. They result from the scattering of electrons off of an atomic or molecular target. They are important for numerous chemical processes in upper atmosphere, space and even biological systems. A contextual background of the existing theoretical methods as well as the newly-developed multiconfigurational propagator tools based on a complex absorbing potential are discussed.
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Affiliation(s)
- Subhasish Das
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Kansapada, Argul, 752050, India
| | - Kousik Samanta
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Kansapada, Argul, 752050, India
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2
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Das S, Samanta K. Investigation of negative-ion resonances using a subspace-projected multiconfigurational electron propagator perturbed with a complex absorbing potential. J Chem Phys 2022; 156:224110. [PMID: 35705417 DOI: 10.1063/5.0089912] [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 transient negative-ion resonances found in scattering experiments are important intermediates in many chemical processes. These metastable states correspond to the continuum part of the Hamiltonian of the projectile-target composite system. Usual bound-state electronic structure methods are not applicable for these. In this work, we develop a subspace-projection method in connection with an electron propagator (EP) defined in terms of a complete-active-space self-consistent-field initial state. The target Hamiltonian (Ĥ) is perturbed by a complex absorbing potential (CAP) for the analytical continuation of the spectrum of Ĥ to complex eigenvalues associated with the continuum states. The resonance is identified as a pole of the EP, which is stable with respect to variations in the strength of the CAP. The projection into a small subspace reduces the size of the complex matrices to be diagonalized, minimizes the computational cost, and affords some insight into the orbitals that are likely to play some role in the capture of the projectile. Two molecular (Πg2N2 - and 2Π CO-) and an atomic shaperesonance (2P Be-) are investigated using this method. The position and width of the resonances are in good agreement with the previously reported values.
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Affiliation(s)
- Subhasish Das
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Argul, Odisha 752050, India
| | - Kousik Samanta
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Argul, Odisha 752050, India
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3
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Jagau TC. Theory of electronic resonances: fundamental aspects and recent advances. Chem Commun (Camb) 2022; 58:5205-5224. [PMID: 35395664 DOI: 10.1039/d1cc07090h] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Electronic resonances are states that are unstable towards loss of electrons. They play critical roles in high-energy environments across chemistry, physics, and biology but are also relevant to processes under ambient conditions that involve unbound electrons. This feature article focuses on complex-variable techniques such as complex scaling and complex absorbing potentials that afford a treatment of electronic resonances in terms of discrete square-integrable eigenstates of non-Hermitian Hamiltonians with complex energy. Fundamental aspects of these techniques as well as their integration into molecular electronic-structure theory are discussed and an overview of some recent developments is given: analytic gradient theory for electronic resonances, the application of rank-reduction techniques and quantum embedding to them, as well as approaches for evaluating partial decay widths.
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Affiliation(s)
- Thomas-C Jagau
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium.
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4
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Varandas AJC. From six to eight Π-electron bare rings of group-XIV elements and beyond: can planarity be deciphered from the "quasi-molecules" they embed? Phys Chem Chem Phys 2022; 24:8488-8507. [PMID: 35343978 DOI: 10.1039/d1cp04130d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ab initio molecular orbital theory is used to study the structures of six and eight π-electron bare rings of group-XIV elements, and even larger [n]annulenes up to C18H18, including some of their mono-, di-, tri-, and tetra-anions. While some of the above rings are planar, others are nonplanar. A much spotlighted case is cyclo-octatetraene (C8H8), which is predicted to be nonplanar together with its heavier group-XIV analogues Si8H8 and Ge8H8, with the solely planar members of its family having the stoichiometric formulas C4Si4H8 and C4Ge4H8. A similar situation arises with the six π-electron bare rings, where benzene and substituted ones up to C3Si3H6 or so are planar, while others are not. However, the explanations encountered in the literature find support in ab initio calculations for such species, often rationalized from distinct calculated features. Using second-order Møller-Plesset perturbation theory and, when affordable (particularly tetratomics, which may allow even higher levels), the coupled-cluster method including single, double, and perturbative triple excitations, a common rationale is suggested based on a novel concept of quasi-molecules or the (3+4)-atom partition scheme. Any criticism of tautology is therefore avoided. The same analysis has also been successfully applied to even larger [n]annulenes, to their mixed family members involving silicon and germanium atoms, and to the C18 carbon ring. Furthermore, it has been extended to annulene anions to check the criteria of the popular Hückel rule for planarity and aromaticity. Exploratory work on cycloarenes is also reported. Besides a partial study of the involved potential energy surfaces, equilibrium geometries and harmonic vibrational frequencies have been calculated anew, for both the parent and the actual prototypes of the quasi-molecules.
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Affiliation(s)
- A J C Varandas
- School of Physics and Physical Engineering, Qufu Normal University, 273165 Qufu, China.,Department of Physics, Universidade Federal do Esp rito Santo, 29075-910 Vitória, Brazil.,Department of Chemistry, and Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal.
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Das S, Sajeev Y, Samanta K. An Electron Propagator Approach Based on a Multiconfigurational Reference State for the Investigation of Negative-Ion Resonances Using a Complex Absorbing Potential Method. J Chem Theory Comput 2020; 16:5024-5034. [PMID: 32568537 DOI: 10.1021/acs.jctc.0c00434] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Negative-ion resonances are important metastable states that result from the collision between an electron and a neutral target. The course of many chemical processes in nature is often dictated by how an intermediate resonance state falls apart. This article reports on the development of an electron propagator (EP) based on a Hamiltonian Ĥ perturbed by a complex absorbing potential (CAP) and a multiconfigurational self-consistent field (MCSCF) initial state to study these resonances. Perturbation of Ĥ by a CAP makes the resonances amenable to a bound-state method like MCSCF. Resonances stand out among the non-resonant states as persistent complex eigenvalues of the perturbed Ĥ when the strength (η) of the CAP is varied. The MCSCF method gives a reliable and accurate description of the target states, especially when the non-dynamical correlations are dominant. The resonance energies are obtained from the poles of the EP. We propose three variants of our EP depending on how the effect of the CAP is introduced. We find that the computationally most efficient variant is the one in which the reference state of the EP is an unperturbed MCSCF wavefunction and a non-zero CAP is defined only on the virtual orbital subspace of the reference state. The onset of the CAP is carefully optimized in order to minimize the artifacts due to reflections from the CAP. An extrapolation method (based on a Padé approximant) and a de-perturbation method are adopted in order to account for the limitations of finite basis sets used and determine the resonance energy in the limit of η → 0. 2P Be-, 2Πg N2-, and 2Π CO- shape resonances are investigated. The position and width of these resonances computed in this study agree well with those reported earlier in the literature.
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Affiliation(s)
- Subhasish Das
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Argul 752050, India
| | - Y Sajeev
- Theoretical Chemistry Section, Bhabha Atomic Research Centre, Mumbai 400085, India
| | - Kousik Samanta
- School of Basic Sciences, Indian Institute of Technology Bhubaneswar, Argul 752050, India
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Phung QM, Komori Y, Yanai T, Sommerfeld T, Ehara M. Combination of a Voronoi-Type Complex Absorbing Potential with the XMS-CASPT2 Method and Pilot Applications. J Chem Theory Comput 2020; 16:2606-2616. [PMID: 32105477 DOI: 10.1021/acs.jctc.9b01032] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Electronic resonances are metastable (N + 1) electron states, in other words, discrete states embedded in an electronic continuum. While great progress has been made for certain types of resonances-for example, temporary anions created by attaching one excess electron to a closed shell neutral-resonances in general remain a great challenge of quantum chemistry because a successful description of the decay requires a balanced description of the bound and continuum aspect of the resonance. Here, a smoothed Voronoi complex absorbing potential (CAP) is combined with the XMS-CASPT2 method, which enables us to address the balance challenge by appropriate choice of the CAS space. To reduce the computational cost, the method is implemented in the projected scheme. In this pilot application, three temporary anions serve as benchmarks: the π* resonance state of formaldehyde; the π* and σ* resonance states of chloroethene as functions of the C-Cl bond dissociation coordinate; and the 4Πu and 2Πu resonance states of N2-. The convergence of the CAP/XMS-CASPT2 results has been systematically examined with respect to the size of the active space. Resonance parameters predicted by the CAP/XMS-CASPT2 method agree well with CAP/SAC-CI results (deviations of about 0.15 eV); however, as expected, CAP/XMS-CASPT2 has clear advantages in the bond dissociation region. The advantages of CAP/XMS-CASPT2 are further demonstrated in the calculations of 4Πu and 2Πu resonance states of N2- including their 3Σu+ and 3Δu parent states. Three of the involved states (2Πu, 3Σu+, and 3Δu) possess multireference character, and CAP/XMS-CASPT2 can easily describe these states with a relatively modest active space.
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Affiliation(s)
- Quan Manh Phung
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Yuki Komori
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
| | - Takeshi Yanai
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan.,Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan.,Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Thomas Sommerfeld
- Department of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
| | - Masahiro Ehara
- Institute for Molecular Science and Research Center for Computational Science, 38 Nishigonaka, Myodaiji, Okazaki 444-8585, Japan.,Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Katsura, Kyoto 615-8520, Japan
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7
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Gulania S, Jagau TC, Krylov AI. EOM-CC guide to Fock-space travel: the C2 edition. Faraday Discuss 2019; 217:514-532. [DOI: 10.1039/c8fd00185e] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electronic structure calculations for C2, C2−, and C22− using the CC/EOM-CC family of methods. Results illustrate that EOM-CCSD provides an attractive alternative to MR approaches.
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Affiliation(s)
- Sahil Gulania
- Department of Chemistry
- University of Southern California
- Los Angeles
- USA
| | - Thomas-C. Jagau
- Department of Chemistry
- University of Munich (LMU)
- 81377 Munich
- Germany
| | - Anna I. Krylov
- Department of Chemistry
- University of Southern California
- Los Angeles
- USA
- The Hamburg Centre for Ultrafast Imaging
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8
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White AF, Epifanovsky E, McCurdy CW, Head-Gordon M. Second order Møller-Plesset and coupled cluster singles and doubles methods with complex basis functions for resonances in electron-molecule scattering. J Chem Phys 2017. [DOI: 10.1063/1.4986950] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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9
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Ehara M, Kanazawa Y, Sommerfeld T. Low-lying π∗ resonances associated with cyano groups: A CAP/SAC-CI study. Chem Phys 2017. [DOI: 10.1016/j.chemphys.2016.09.033] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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10
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Kanazawa Y, Ehara M, Sommerfeld T. Low-Lying π* Resonances of Standard and Rare DNA and RNA Bases Studied by the Projected CAP/SAC–CI Method. J Phys Chem A 2016; 120:1545-53. [DOI: 10.1021/acs.jpca.5b12190] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yuki Kanazawa
- SOKENDAI, the Graduate University for Advanced Studies, Nishigonaka, Myodaiji, Okazaki 444-8585, Japan
- Institute for Molecular Science and Research Center for Computational Science, Nishigonaka, Myodaiji, Okazaki 444-8585, Japan
| | - Masahiro Ehara
- SOKENDAI, the Graduate University for Advanced Studies, Nishigonaka, Myodaiji, Okazaki 444-8585, Japan
- Institute for Molecular Science and Research Center for Computational Science, Nishigonaka, Myodaiji, Okazaki 444-8585, Japan
| | - Thomas Sommerfeld
- Department
of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
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11
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Sommerfeld T, Ehara M. Complex Absorbing Potentials with Voronoi Isosurfaces Wrapping Perfectly around Molecules. J Chem Theory Comput 2015; 11:4627-33. [DOI: 10.1021/acs.jctc.5b00465] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Thomas Sommerfeld
- Department
of Chemistry and Physics, Southeastern Louisiana University, SLU 10878, Hammond, Louisiana 70402, United States
| | - Masahiro Ehara
- Institute for
Molecular Science, Research Center for Computational Science, Myodai-ji, Okazaki 444-8585, Japan
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12
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Ehara M, Fukuda R, Sommerfeld T. Projected CAP/SAC-CI method with smooth Voronoi potential for calculating resonance states. J Comput Chem 2015; 37:242-9. [DOI: 10.1002/jcc.24010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Revised: 06/18/2015] [Accepted: 06/20/2015] [Indexed: 01/06/2023]
Affiliation(s)
- Masahiro Ehara
- Institute for Molecular Science and Research Center for Computational Science; 38 Nishigonaka, Myodaiji Okazaki 444-8585 Japan
- Elements Strategy Initiative for Catalysts and Batteries (ESICB); Kyoto University; Katsura Kyoto 615-8520 Japan
| | - Ryoichi Fukuda
- Institute for Molecular Science and Research Center for Computational Science; 38 Nishigonaka, Myodaiji Okazaki 444-8585 Japan
- Elements Strategy Initiative for Catalysts and Batteries (ESICB); Kyoto University; Katsura Kyoto 615-8520 Japan
| | - Thomas Sommerfeld
- Department of Chemistry and Physics; Southeastern Louisiana University; SLU 10878 Hammond Louisiana 70402
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13
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Sabzyan H, Keshavarz E, Noorisafa Z. Diatomic dications and dianions. JOURNAL OF THE IRANIAN CHEMICAL SOCIETY 2013. [DOI: 10.1007/s13738-013-0359-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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14
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Sokolov AY, Magers DB, Wu JI, Allen WD, Schleyer PVR, Schaefer HF. Free Cyclooctatetraene Dianion: Planarity, Aromaticity, and Theoretical Challenges. J Chem Theory Comput 2013; 9:4436-43. [DOI: 10.1021/ct400642y] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Alexander Yu. Sokolov
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
| | - D. Brandon Magers
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
| | - Judy I. Wu
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
| | - Wesley D. Allen
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
| | - Paul v. R. Schleyer
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
| | - Henry F. Schaefer
- Center for Computational Quantum
Chemistry, The University of Georgia, Athens, Georgia 30602, United States
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15
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Ehara M, Sommerfeld T. CAP/SAC-CI method for calculating resonance states of metastable anions. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.03.104] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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16
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Chakraborty A, Giri S, Duley S, Anoop A, Bultinck P, Chattaraj PK. Aromaticity in all-metal annular systems: the counter-ion effect. Phys Chem Chem Phys 2011; 13:14865-78. [DOI: 10.1039/c1cp21430f] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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17
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Szentpály LV. Universal Method to Calculate the Stability, Electronegativity, and Hardness of Dianions. J Phys Chem A 2010; 114:10891-6. [DOI: 10.1021/jp107177d] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- László von Szentpály
- Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
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18
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Halmová G, Tennyson J. Resonances in electron-impact electron detachment of C2-. PHYSICAL REVIEW LETTERS 2008; 100:213202. [PMID: 18518603 DOI: 10.1103/physrevlett.100.213202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2007] [Indexed: 05/26/2023]
Abstract
Molecular R-matrix with pseudostate calculations are reported for the electron-impact ionization cross section of the carbon dimer anion. A (1)Sigma_(g)(+) resonance is found near the detachment threshold and two further resonances, of (3)Pi_(g) and (1)Pi_(g) symmetry, are found near 10 eV close to the structures observed experimentally. These unusual shape resonances are a result of the competition between the repulsive Coulomb interaction and the large, attractive polarizability of C2-. Use of the Born approximation to allow for higher partial waves gives a total cross section close to that observed experimentally.
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Affiliation(s)
- Gabriela Halmová
- Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom
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19
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Pal S, Sajeev Y, Vaval N. Analytically continued Fock space multi-reference coupled-cluster theory: Application to the shape resonance. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2006.07.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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20
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Sajeev Y, Pal * S. A general formalism of the Fock space multireference coupled cluster method for investigating molecular electronic resonances. Mol Phys 2005. [DOI: 10.1080/00268970500084158] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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21
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Ehrler OT, Furche F, Weber JM, Kappes MM. Photoelectron spectroscopy of fullerene dianions C762−, C782−, and C842−. J Chem Phys 2005; 122:094321. [PMID: 15836142 DOI: 10.1063/1.1859272] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report laser photoelectron spectra of the doubly negatively charged fullerenes C(76) (2-), C(78) (2-), and C(84) (2-) at 2.33, 3.49, and 4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment energies, as well as estimates for the repulsive Coulomb barriers are obtained. These results are discussed in the context of electrostatic models. They reveal that fullerenes are similar to conducting spheres, with electronic properties scaling with their size. The experimental spectra are compared with the accessible excited states of the respective singly charged product ions calculated in the framework of time dependent density functional theory.
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Affiliation(s)
- Oli T Ehrler
- Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany
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22
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Jung Y, Heine T, Schleyer PVR, Head-Gordon M. Aromaticity of Four-Membered-Ring 6π-Electron Systems: N2S2 and Li2C4H4. J Am Chem Soc 2004; 126:3132-8. [PMID: 15012143 DOI: 10.1021/ja0351490] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
N(2)S(2) is a four-membered-ring system with 6pi electrons. While earlier proposals considered N(2)S(2) to be aromatic, recent electronic structure calculations claimed that N(2)S(2) is a singlet diradical. Our careful reexamination does not support this assertion. N(2)S(2) is closed shell and aromatic since it satisfies all three generally accepted criteria for aromaticity: energetic (stability), structural (planarity with equal bond lengths), and magnetic (negative nucleus-independent chemical shift due to the pi electrons). These characteristics as well as the electronic structure of N(2)S(2) are compared with those for an isoelectronic pi system, Li(2)C(4)H(4), motivated by theoretical and recent experimental investigations that confirmed its aromaticity. However, N(2)S(2) and Li(2)C(4)H(4) are both essentially 2pi-electron aromatic systems with a formal N-S (C-C) bond order of 1.25 even though they both have 6pi electrons. This is because four of the six pi electrons occupy the nonbonding pi HOMOs and only two electrons participate effectively in the aromatic stabilization. However, wave function analysis shows relatively large LUMO occupation numbers; this antibonding effect can be said to reduce the aromatic character by approximately 7% and 4% for N(2)S(2) and Li(2)C(4)H(4), respectively.
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Affiliation(s)
- Yousung Jung
- Department of Chemistry, University of California at Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, USA
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23
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Santra R, Cederbaum LS. Complex absorbing potentials in the framework of electron propagator theory. I. General formalism. J Chem Phys 2002. [DOI: 10.1063/1.1501903] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Abstract
Isolated dianions of cyclooctatetraene and cyclobutadiene are, despite their aromatic character, unstable with respect to electron loss. Here we present the first ab initio study of the autodetachment lifetimes of several "aromatic" dianions. In particular, we investigate whether aromatic pi systems are associated with an enhanced stability with respect to electron loss and whether cross-conjugated (Y-aromatic) hydrocarbon dianions possess longer lifetimes than their linear-conjugated isomers. Moreover, our results are compared with bound state calculations for these metastable dianions, allowing us to analyze the validity of the latter approach. All considered, hydrocarbon dianions are found to possess surprisingly short autodetachment lifetimes on the order of a few femtoseconds, and therefore only electron scattering techniques seem to be capable of observing these species in the gas phase. The trends of the computed energies and lifetimes are best understood in terms of the mutual Coulomb repulsion of the extra charges. Small gas phase dianions can only be stable if the excess electrons can localize at least at two subgroups of high local electron affinity. Adding both extra electrons into one delocalized pi system leads to a very unstable species, and thus especially those structures associated with pronounced aromaticity are found to show high energies and short lifetimes.
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Affiliation(s)
- Thomas Sommerfeld
- Theoretische Chemie, Universität Heidelberg Im Neuenheimer Feld 229, 69120 Heidelberg, Germany.
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26
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Affiliation(s)
- Andreas Dreuw
- Theoretische Chemie, Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany.
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27
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Santra R, Cederbaum LS. An efficient combination of computational techniques for investigating electronic resonance states in molecules. J Chem Phys 2001. [DOI: 10.1063/1.1405117] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Andersen LH, Bak J, Boyé S, Clausen M, Hovgaard M, Jensen MJ, Lapierre A, Seiersen K. Resonant and nonresonant electron impact detachment of CN− and BO−. J Chem Phys 2001. [DOI: 10.1063/1.1388556] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Affiliation(s)
- Thomas Sommerfeld
- Theoretische Chemie, Universität Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
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Sommerfeld T. Resonance states of atomic Di-anions. PHYSICAL REVIEW LETTERS 2000; 85:956-959. [PMID: 10991448 DOI: 10.1103/physrevlett.85.956] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2000] [Indexed: 05/23/2023]
Abstract
Metastable states of O (2-), S (2-), B (2-), and Al (2-) are studied in the framework of the complex absorbing potential method using highly correlated multireference configuration interaction wave functions. The first row species O (2-) and B (2-) are found to be broad resonances showing widths of roughly 1.7 eV, whereas the second row systems S (2-) and Al (2-) possess widths clearly smaller than 1 eV. The identified resonance states are compared to the fundamental H (2-) resonance, and the relationship with recent electron scattering experiments is discussed.
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Affiliation(s)
- T Sommerfeld
- Theoretische Chemie, Universitat Heidelberg, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
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