The orbital-specific virtual local triples correction: OSV-L(T)

Abstract

A local method based on orbital specific virtuals (OSVs) for calculating the perturbative triples correction in local coupled cluster calculations is presented. In contrast to the previous approach based on projected atomic orbitals (PAOs), described by Schütz [J. Chem. Phys. 113, 9986 (2000)], the new scheme works without any ad hoc truncations of the virtual space to domains. A single threshold defines the pair and triple specific virtual spaces completely and automatically. It is demonstrated that the computational cost of the method scales linearly with molecular size. Employing the recommended threshold a similar fraction of the correlation energy is recovered as with the original PAO method at a somewhat lower cost. A benchmark for 52 reactions demonstrates that for reaction energies the intrinsic accuracy of the coupled cluster with singles and doubles excitations and a perturbative treatment of triples excitations method can be reached by OSV-local coupled cluster theory with singles and doubles and perturbative triples, provided a MP2 correction is applied that accounts for basis set incompleteness errors as well as for remaining domain errors. As an application example the interaction energies of the guanine-cytosine dimers in the Watson-Crick and stacked arrangements are investigated at the level of local coupled cluster theory with singles and doubles and perturbative triples. Based on these calculations we propose new complete-basis-set-limit estimates for these interaction energies at this level of theory.

Efficient and accurate treatment of weak pairs in local CCSD(T) calculations

“…In order to defeat this unfavorably high scaling wall and to make the method also applicable to extended molecular systems, local CCSD(T) methods were developed during the past fifteen years. [3][4][5][6][7][8][9] The term "local" here implies the formulation of CCSD(T) in terms of spatially localized occupied and virtual molecular orbitals (MOs), rather than the commonly used delocalized and a) Electronic mail: martin.schuetz@chemie.uni-regensburg.de symmetry-adapted canonical orbitals diagonalizing the Fock matrix. Local MOs spanning the occupied space (LMOs) are usually obtained by applying a localization procedure such as Pipek-Mezey 10 or Boys 11 to the occupied canonical orbitals obtained from the preceding Hartree-Fock calculation.…”

“…Local MOs spanning the occupied space (LMOs) are usually obtained by applying a localization procedure such as Pipek-Mezey 10 or Boys 11 to the occupied canonical orbitals obtained from the preceding Hartree-Fock calculation. For the virtual space, e.g., projected atomic orbitals (PAOs), [12][13][14][15][16][17] orbital specific virtuals (OSVs), 6,[18][19][20][21] or pair natural orbitals (PNOs) [22][23][24][25][26][27][28][29] can be used, either exclusively, or also in combination.…”

Communication: An improved linear scaling perturbative triples correction for the domain based local pair-natural orbital based singles and doubles coupled cluster method [DLPNO-CCSD(T)]

“…To overcome this difficulty, orbital-specific virtual (OSV) orbitals were used to reduce the virtual space of each triple. 22 Furthermore, Schmitz and Hättig introduced the Laplace transformation (LT) technique 23 in their recent PNO-CCSD(T) method. 25,26 The storage bottleneck of the triples amplitudes is completely avoided by using the LT technique.…”

Communication: Improved pair approximations in local coupled-cluster methods

“…In practice, non-orthogonal virtual orbitals [projected atomic orbitals (PAOs), [1][2][3][4] orbital specific virtuals (OSVs), [41][42][43] or PNOs [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] ] are used, which leads to additional contractions with overlap matrices, but the general arguments are not affected.…”