Schuetz, Martin and Masur, Oliver and Usvyat, Denis (2014) Efficient and accurate treatment of weak pairs in local CCSD(T) calculations. II. Beyond the ring approximation. JOURNAL OF CHEMICAL PHYSICS, 140 (24): 244107. ISSN 0021-9606, 1089-7690
Full text not available from this repository. (Request a copy)Abstract
In order to arrive at linear scaling of the computational cost with molecular size, local coupled cluster methods discriminate pairs of local molecular orbitals according to the spatial separation R of the latter. Only strong pairs are treated at the full coupled cluster level, whereas for weak pairs a lower level of theory (usually Moller-Plesset perturbation theory of second order, MP2) is used. Yet an MP2 treatment of weak pairs is inadequate in certain situations (for example, for describing pi-stacking), which calls for an improved but still inexpensive method for dealing with the weak pairs. In a previous contribution, we proposed as a substituent for MP2 the LrCCD3 method, which is based on ring coupled cluster doubles (ring-CCD) and includes all third-order diagrams with energy contributions decaying not quicker than R-6. In the present work, we explore a still more accurate method, which is based on the same principles. It turned out to be essential to abandon the restriction to ring-CCD, i.e., to include further CCD diagrams beyond the ring approximation. The occurring intermediates turn out to be formally very similar to LMP2 density matrices, such that an efficient evaluation of these non-ring CCD diagrams is possible. Furthermore, a computationally cheap a posteriori estimate for the fourth-order singles contribution to the weak pair energy, which also exhibits a decay behavior of R-6, is introduced. The resulting method, denoted as LCCD[S]-R-6, indeed provides a substantial improvement in accuracy over the previous LrCCD3 method at a relatively modest additional computational cost. (C) 2014 AIP Publishing LLC.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | ELECTRON CORRELATION METHODS; PLESSET PERTURBATION-THEORY; BASIS-SETS; CONFIGURATION-INTERACTION; INTERACTION ENERGIES; WAVE-FUNCTIONS; PNO-CI; ORBITALS; TRIPLES; FORMULATION; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Research Group Theoretical Chemistry |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 17 Oct 2019 12:58 |
| Last Modified: | 17 Oct 2019 12:58 |
| URI: | https://pred.uni-regensburg.de/id/eprint/10004 |
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