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Varandas AJC, Rocha CMR. Cn ( n=2-4): current status. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:rsta.2017.0145. [PMID: 29431687 PMCID: PMC5805914 DOI: 10.1098/rsta.2017.0145] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/27/2017] [Indexed: 05/28/2023]
Abstract
The major aspects of the C2, C3 and C4 elemental carbon clusters are surveyed. For C2, a brief analysis of its current status is presented. Regarding C3, the most recent results obtained in our group are reviewed with emphasis on modelling its potential energy surface which is particularly complicated due to the presence of multiple conical intersections. As for C4, the most stable isomeric forms of both triplet and singlet spin states and their possible interconversion pathways are examined afresh by means of accurate ab initio calculations. The main strategies for modelling the ground triplet C4 potential are also discussed. Starting from a truncated cluster expansion and a previously reported DMBE form for C3, an approximate four-body term is calibrated from the ab initio energies. The final six-dimensional global DMBE form so obtained reproduces all known topographical aspects while providing an accurate description of the C4 linear-rhombic isomerization pathway. It is therefore commended for both spectroscopic and reaction dynamics studies.This article is part of the theme issue 'Modern theoretical chemistry'.
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Affiliation(s)
- A J C Varandas
- Department of Chemistry and Coimbra Chemistry Center, University of Coimbra 3004-535 Coimbra, Portugal
| | - C M R Rocha
- Department of Chemistry and Coimbra Chemistry Center, University of Coimbra 3004-535 Coimbra, Portugal
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Varandas AJC. Straightening the Hierarchical Staircase for Basis Set Extrapolations: A Low-Cost Approach to High-Accuracy Computational Chemistry. Annu Rev Phys Chem 2018; 69:177-203. [PMID: 29394151 DOI: 10.1146/annurev-physchem-050317-021148] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Because the one-electron basis set limit is difficult to reach in correlated post-Hartree-Fock ab initio calculations, the low-cost route of using methods that extrapolate to the estimated basis set limit attracts immediate interest. The situation is somewhat more satisfactory at the Hartree-Fock level because numerical calculation of the energy is often affordable at nearly converged basis set levels. Still, extrapolation schemes for the Hartree-Fock energy are addressed here, although the focus is on the more slowly convergent and computationally demanding correlation energy. Because they are frequently based on the gold-standard coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)], correlated calculations are often affordable only with the smallest basis sets, and hence single-level extrapolations from one raw energy could attain maximum usefulness. This possibility is examined. Whenever possible, this review uses raw data from second-order Møller-Plesset perturbation theory, as well as CCSD, CCSD(T), and multireference configuration interaction methods. Inescapably, the emphasis is on work done by the author's research group. Certain issues in need of further research or review are pinpointed.
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Affiliation(s)
- António J C Varandas
- Coimbra Chemistry Center and Department of Chemistry, University of Coimbra, Coimbra 3004-535, Portugal;
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Varandas AJC. CBS extrapolation in electronic structure pushed to the end: a revival of minimal and sub-minimal basis sets. Phys Chem Chem Phys 2018; 20:22084-22098. [DOI: 10.1039/c8cp02932f] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The complete basis set (CBS) limit is secluded in calculations of electronic structure, and hence CBS extrapolation draws immediate attention.
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Affiliation(s)
- A. J. C. Varandas
- School of Physics and Physical Engineering
- Qufu Normal University
- 273165 Qufu
- China
- Departamento de Química, and Centro de Química
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Varandas AJC, Martínez González M, Montero-Cabrera LA, Garcia de la Vega JM. Assessing How Correlated Molecular Orbital Calculations Can Perform versus Kohn-Sham DFT: Barrier Heights/Isomerizations. Chemistry 2017; 23:9122-9129. [PMID: 28380281 DOI: 10.1002/chem.201700928] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Indexed: 11/06/2022]
Abstract
To assess the title issue, 38 hydrogen transfer barrier heights and 38 non-hydrogen transfer barrier heights/isomerizations extracted from extensive databases have been considered, in addition to 4 2 p-isomerization reactions and 6 others for large organic molecules. All Kohn-Sham DFT calculations have employed the popular M06-2X functional, whereas the correlated molecular orbital (MO)-based ones are from single-reference MP2 and CCSD(T) methods. They have all utilized the same basis sets, with raw MO energies subsequently extrapolated to the complete basis set limit without additional cost. MP2 calculations are found to be as cost-effective as DFT ones and often slightly more, while showing a satisfactory accuracy when compared with the reference data. Although the focus is on barrier heights, the results may bear broader implications, in that one may see successes and difficulties of DFT when compared with traditional MO theories for the same data.
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Affiliation(s)
- António J C Varandas
- Departamento de Química, and Centro de Química, Universidade de Coimbra, 3004-535, Coimbra, Portugal
| | - Marco Martínez González
- Departamento de Química, and Centro de Química, Universidade de Coimbra, 3004-535, Coimbra, Portugal.,Universidad de La Habana, Facultad de Química, calle San Lázaro sn., 10400, La Habana, Cuba
| | - Luis A Montero-Cabrera
- Universidad de La Habana, Facultad de Química, calle San Lázaro sn., 10400, La Habana, Cuba
| | - José M Garcia de la Vega
- Departamento de Química, and Centro de Química, Universidade de Coimbra, 3004-535, Coimbra, Portugal.,Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain
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Extrapolation of Hartree–Fock and multiconfiguration self-consistent-field energies to the complete basis set limit. Theor Chem Acc 2016. [DOI: 10.1007/s00214-016-2016-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Neves RPP, Fernandes PA, Varandas AJC, Ramos MJ. Benchmarking of Density Functionals for the Accurate Description of Thiol-Disulfide Exchange. J Chem Theory Comput 2015; 10:4842-56. [PMID: 26584371 DOI: 10.1021/ct500840f] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A set of 92 density functionals was employed to accurately characterize thiol-disulfide exchange. The properties we have benchmarked throughout the study include the geometry of a 15 atoms model system, the potential energy surface, the activation barrier, and the energy of reaction for thiol-disulfide exchange. Reference energies were determined at the CCSD(T)/CBS//MP2/aug-cc-pVDZ level of theory, and reference geometries were calculated at the MP2/aug-cc-pVTZ level. M11-L, M06-2X, M06-HF, N12-SX, PBE1PBE, PBEh1PBE, and OHSE2PBE described better the geometry of the model system, with average deviations of 0.06 Å in bond lengths (0.06 Å in bond-breaking lengths) and 1.9° in bond angles. On the other hand, the potential energy surface and its gradient were more accurately described by the hybrid density functional BHandH, closely followed by mPW1N, mPW1K, and mPWB1K. The barrier height and energy of reaction were better reproduced by the BMK and M06-2X functionals (deviations of 0.17 and 0.07 kcal·mol(-1), respectively) for a set of 10 Pople's basis sets. MN12-SX and M11-L showed very good results for the widely used 6-311++G(2d,2p) basis set, with deviations of 0.02 and 0.05 kcal·mol(-1), respectively. We studied the effect of the split-valence, diffuse, and polarized functions in the activation barrier of thiol-disulfide exchange, for a set of 10 Pople's basis sets. While increasing the splitting and polarization may increase the activation barrier in approximately 1 kcal·mol(-1), diffuse functions generally contribute to decreasing it no more than 0.10 kcal·mol(-1). In general, 13 functionals provided energies within 1 kcal·mol(-1) of the reference value. The BB1K density functional is one of the best density functionals to characterize thiol-disulfide exchange reactions; however, several density functionals with modified Perdew-Wang exchange and about 40% Hartree-Fock exchange, such as mPW1K, mPW1N, and mPWB1K, show a good performance, too.
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Affiliation(s)
- Rui P P Neves
- REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal
| | - Pedro A Fernandes
- REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal
| | - António J C Varandas
- Departamento de Química, and Centro de Química, Universidade de Coimbra , 3004-535 Coimbra, Portugal
| | - Maria J Ramos
- REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal
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Teixidor MM, Varandas AJC. Quantum dynamics study on the CHIPR potential energy surface for the hydroperoxyl radical: the reactions O + OH⇋O2 + H. J Chem Phys 2015; 142:014309. [PMID: 25573563 DOI: 10.1063/1.4905292] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Quantum scattering calculations of the O((3)P)+OH((2)Π)⇌O2((3)Σg (-))+H((2)S) reactions are presented using the combined-hyperbolic-inverse-power-representation potential energy surface [A. J. C. Varandas, J. Chem. Phys. 138, 134117 (2013)], which employs a realistic, ab initio-based, description of both the valence and long-range interactions. The calculations have been performed with the ABC time-independent quantum reactive scattering computer program based on hyperspherical coordinates. The reactivity of both arrangements has been investigated, with particular attention paid to the effects of vibrational excitation. By using the J-shifting approximation, rate constants are also reported for both the title reactions.
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Affiliation(s)
- Marc Moix Teixidor
- Departamento de Química and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - António J C Varandas
- Departamento de Química and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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Torrent-Sucarrat M, Varandas AJC. Carbon Dioxide Capture with the Ozone-like Polynitrogen Molecule Li3N3. J Phys Chem A 2014; 118:12256-61. [DOI: 10.1021/jp509933x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Miquel Torrent-Sucarrat
- Departamento
de Química
and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
| | - António J. C. Varandas
- Departamento
de Química
and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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Sun Y, Cao H, Han D, Li J, He M. Reactions of n-butyl acrylate and ethyl methacrylate with ozone in the gas phase. COMPUT THEOR CHEM 2014. [DOI: 10.1016/j.comptc.2014.04.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Varandas A. On carbon dioxide capture: An accurate ab initio study of the Li3N+CO2 insertion reaction. COMPUT THEOR CHEM 2014. [DOI: 10.1016/j.comptc.2014.02.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Varandas AJC. Is HO3− multiple-minimum and floppy? Covalent to van der Waals isomerization and bond rupture of a peculiar anion. Phys Chem Chem Phys 2014; 16:16997-7007. [DOI: 10.1039/c4cp01757a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The HO3− anion is multiple-minimum and floppy: the two main isomers and isomerization barrier all lie quite below dissociation.
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Affiliation(s)
- A. J. C. Varandas
- Departamento de Química
- and Centro de Química
- Universidade de Coimbra
- 3004-535 Coimbra, Portugal
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Zhou Y, Hu H, Li L, Hou H, Wang B. Ab initio study of the elusive HO3(X2A″) radical and the reaction. COMPUT THEOR CHEM 2013. [DOI: 10.1016/j.comptc.2013.10.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Viegas LP, Varandas AJC. Coupled‐cluster reaction barriers of : An application of the coupled‐cluster//Kohn–Sham density functional theory model chemistry. J Comput Chem 2013; 35:507-17. [DOI: 10.1002/jcc.23458] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Revised: 09/06/2013] [Accepted: 09/12/2013] [Indexed: 11/10/2022]
Affiliation(s)
- Luís P. Viegas
- Departamento de QuímicaUniversidade de Coimbra3004‐535Coimbra Portugal
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Galvão BRL, Varandas AJC. Accurate study of the two lowest singlet states of HN3: stationary structures and energetics at the MRCI complete basis set limit. J Phys Chem A 2013; 117:4044-50. [PMID: 23586743 DOI: 10.1021/jp402090s] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The two lowest singlet potential energy surfaces of the hydrazoic acid are explored using high-level quantum chemistry calculations, revealing isomeric forms, transition states, and a new path for the nitrogen ring-closing mechanism in the ground state. The reaction of cyc-N3 with hydrogen is shown to proceed through a barrierless path that dissociates to N2 + NH((1)Δ) without reaching the HN3 global minimum. Several intersections between the two states are localized for both N3 isomers near the N3 + H dissociation. The energies of stationary structures and dissociation asymptotes are obtained with the multireference configuration interaction method at the complete basis set limit. A comparison with recent experimental data regarding the H-N3 bond strength and the dissociation barrier in the excited state shows that the present results are of chemical accuracy (~1 kcal mol(-1)).
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Affiliation(s)
- B R L Galvão
- Departamento de Quı́mica, Universidade de Coimbra, 3004-535 Coimbra, Portugal
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