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Coupled cluster
About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.
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TL;DR: The relative energies of the YMPJ conformer database of the 20 proteinogenic amino acids, with N- and C-termination, have been re-evaluated using explicitly correlated coupled cluster methods and should be useful in the parametrization and validation of molecular mechanics force fields and other low-cost methods.
Abstract: The relative energies of the YMPJ conformer database of the 20 proteinogenic amino acids, with N- and C-termination, have been re-evaluated using explicitly correlated coupled cluster methods. Lower-cost ab initio methods such as MP2-F12 and CCSD-F12b actually are outperformed by double-hybrid DFT functionals; in particular, the DSD-PBEP86-NL double hybrid performs well enough to serve as a secondary standard. Among range-separated hybrids, ωB97X-V performs well, while B3LYP-D3BJ does surprisingly well among traditional DFT functionals. Treatment of dispersion is important for the DFT functionals; for the YMPJ set, D3BJ generally works as well as the NL nonlocal dispersion functional. Basis set sensitivity for DFT calculations on these conformers is weak enough that def2-TZVP is generally adequate. For conformer corrections to heats of formation, B3LYP-D3BJ and especially DSD-PBEP86-D3BJ or DSD-PBEP86-NL are adequate for all but the most exacting applications. The revised geometries and energetics for the...
99 citations
TL;DR: The previously developed active-space coupled-cluster and equation-of-motion CC methods are extended to radicals and other open-shell systems by combining them with the electron attached and ionized EOMCC approaches, capable of providing a highly accurate description of the electronic spectra of radical systems.
Abstract: The previously developed active-space coupled-cluster (CC) and equation-of-motion (EOM) CC methods are extended to radicals and other open-shell systems by combining them with the electron attached (EA) and ionized (IP) EOMCC approaches. As illustrated by the calculations for the CH and OH radicals, the resulting EA-EOMCCSDt and IP-EOMCCSDt theories are capable of providing a highly accurate description of the electronic spectra of radical systems, including excited states displaying a manifestly multideterminantal nature, with the low costs that are not much greater that those characterizing the standard EOMCC singles and doubles method.
99 citations
TL;DR: In this paper, the authors proposed renormalized and completely renormalised CCSDT(Q) methods, which result from the method of moments of coupled-cluster equations, have been implemented and applied to the potential energy curve of N2.
99 citations
TL;DR: In this article, the relative energy of the second-row atoms of the HSO and SOH isomers using Hartree−Fock, coupled cluster with single and double excitation, and coupled clusters with single, double, and perturbative triple excitation levels of theory was determined for each species.
Abstract: The tight d-augmented correlation consistent basis sets, cc-pV(n+d)Z, and standard correlation consistent basis sets, cc-pVnZ, where n = D(2), T(3), Q(4), and 5, for the second-row atoms have been used to re-examine the relative energy of the HSO and SOH isomers using Hartree−Fock, coupled cluster with single and double excitation, and coupled cluster with single, double, and perturbative triple excitation levels of theory. Geometries, dissociation energies, and vibrational frequencies have also been determined for each species. The relative energies of the two isomers converge more rapidly and smoothly for the new tight d-augmented sets than for the standard sets. The impact of the tight d function is most significant upon dissociation energies at the double-ζ and triple-ζ levels for HSO, with differences of 5.46 and 2.57 kcal/mol, respectively, and less significant for SOH, with differences of 1.90 and 1.20 kcal/mol. The impact of the additional d functions in the basis set upon vibrational frequencies ...
98 citations
TL;DR: In this article, the optimized structures and harmonic frequencies for the transition states and intermediates on the ground state potential energy surfaces of ethylenes, including C2H4, C2D4, D2CCH2, and cis-and trans-HDCCDH, related to the molecular and atomic hydrogen elimination channels of photodissociation in VUV were characterized at the B3LYP/6-311G(d,p) level.
Abstract: The optimized structures and harmonic frequencies for the transition states and intermediates on the ground state potential energy surfaces of ethylenes, including C2H4, C2D4, D2CCH2, and cis- and trans-HDCCDH, related to the molecular and atomic hydrogen elimination channels of photodissociation in VUV were characterized at the B3LYP/6-311G(d,p) level. The coupled cluster method, CCSD(T)/6-311+G(3df,2p), was employed to calculate the corresponding energies with the zero-point energy corrections by the B3LYP/6-311G(d,p) approach. Ethylidene was found to be an intermediate in the 1,2-H2 elimination channel. The barrier for the 1,1-H2 elimination was computed to be the lowest (4.10–4.16 eV), while the 1,2-H2 elimination and H loss channels have barriers of a similar height (4.70–4.80 eV). The rate constant for each elementary step of ethylene photodissociation at 193 and 157 nm was calculated according to the RRKM theory based on the ab initio surfaces. The rate equations were subsequently solved, and thus ...
98 citations