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Ab initio quantum chemistry methods

About: Ab initio quantum chemistry methods is a research topic. Over the lifetime, 24413 publications have been published within this topic receiving 740820 citations. The topic is also known as: Ab initio method & Ab initio molecular orbital method.


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TL;DR: In this paper, an all-atom CFF93 force field for polycarbonates based on ab initio calculations is reported, and the force field parameters are derived by fitting to quantum mechanical total energies, first and second derivatives of total energies and electrostatic potentials, all generated from AB initio quantum mechanical calculations on model compounds at HF/6-31GS level of theory.
Abstract: An all-atom CFF93 force field for polycarbonates based on ab initio calculations is reported. Force field parameters are derived by fitting to quantum mechanical total energies, first and second derivatives of total energies, and electrostatic potentials, all generated from ab initio quantum mechanical calculations on model compounds at HF/6-31GS level of theory. Valence parameters and ab initiocharges are then scaled to correct for differences between experiment and the Hartree-Fock approximation. The van der Waals parameters and the scaling factors for atomic partial charges are determined from crystal structures. Based on the force field, molecular mechanics calculations are performed for several model compounds, and the results are compared with experimental values and with the results of the ab initio calculations.

933 citations

Journal ArticleDOI
TL;DR: In this paper, the authors reported ab initio calculations of the two-dimensional systems (MoS and NbSe) and compared them with the electronic structure of the three-dimensional analogue of graphene.
Abstract: We report on ab initio calculations of the two-dimensional systems ${\text{MoS}}_{2}$ and ${\text{NbSe}}_{2}$, which recently were synthesized. We find that two-dimensional ${\text{MoS}}_{2}$ is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that ${\text{NbSe}}_{2}$ is a metal, which is similar to the three-dimensional analog of this compound. We further computed the electronic structure of the two-dimensional hexagonal (graphene-like) lattices of Si and Ge and compared them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, also known as silicene, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.

924 citations

Journal ArticleDOI
TL;DR: Modifications to the Cornell et al. force field are tested in molecular dynamics simulations of mononucleosides and double helices of DNA and RNA (to assess helical and sequence specific structural properties) and lead to improved agreement with experimental data.
Abstract: We have examined some subtle parameter modifications to the Cornell et al. force field, which has proven quite successful in reproducing nucleic acid properties, but whose C2'-endo sugar pucker phase and helical repeat for B DNA appear to be somewhat underestimated. Encouragingly, the addition of a single V2 term involving the atoms C(sp3)-O-(sp3)-C(sp3)-N(sp2), which can be nicely rationalized because of the anomeric effect (lone pairs on oxygen are preferentially oriented relative to the electron withdrawing N), brings the sugar pucker phase of C2'-endo sugars to near perfect agreement with ab initio calculations (W near 162 degrees). Secondly, the use of high level ab initio calculations on entire nucleosides (in contrast to smaller model systems necessitated in 1994-95 by computer limitations) lets one improve the chi torsional potential for nucleic acids. Finally, the O(sp3)-C(sp3)- C(sp3)-O(sp3) V2 torsional potential has been empirically adjusted to reproduce the ab initio calculated relative energy of C2'-endo and C3'-endo nucleosides. These modifications are tested in molecular dynamics simulations of mononucleosides (to assess sugar pucker percentages) and double helices of DNA and RNA (to assess helical and sequence specific structural properties). In both areas, the modified force field leads to improved agreement with experimental data.

915 citations

Journal ArticleDOI
TL;DR: In this article, two new schemes for computing molecular total atomization energies (TAEs) and/or heats of formation (ΔHf∘) of first and second-row compounds to very high accuracy are presented.
Abstract: Two new schemes for computing molecular total atomization energies (TAEs) and/or heats of formation (ΔHf∘) of first- and second-row compounds to very high accuracy are presented. The more affordable scheme, W1 (Weizmann-1) theory, yields a mean absolute error of 0.30 kcal/mol and includes only a single, molecule-independent, empirical parameter. It requires CCSD (coupled cluster with all single and double substitutions) calculations in spdf and spdfg basis sets, while CCSD(T) (i.e., CCSD with a quasiperturbative treatment of connected triple excitations) calculations are only required in spd and spdf basis sets. On workstation computers and using conventional coupled cluster algorithms, systems as large as benzene can be treated, while larger systems are feasible using direct coupled cluster methods. The more rigorous scheme, W2 (Weizmann-2) theory, contains no empirical parameters at all and yields a mean absolute error of 0.23 kcal/mol, which is lowered to 0.18 kcal/mol for molecules dominated by dynami...

911 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023103
2022262
2021281
2020354
2019414
2018437