Calculation of dispersion interactions with the geminal-based ring Coupled Cluster Doubles method
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Calculation of dispersion interactions with the geminal‑based ring Coupled Cluster Doubles method Á. Margócsy1,2 · Á. Szabados2 Received: 28 March 2020 / Accepted: 10 June 2020 © The Author(s) 2020
Abstract The performance of the recently developed multi-reference extension of ring coupled cluster doubles is investigated for dispersion energy calculations, applied to the generalized valence bond wave function. The leading-order contribution to the dispersion energy is shown to have the correct asymptotic behaviour. Illustrative calculations on noble gas dimers are presented. Keywords Coupled Cluster Doubles · Ring approximation · Dispersion interaction · Generalized valence bond · Cumulants
1 Introduction Calculation of dispersion energy between atoms or molecules is a long-standing problem of quantum chemistry. Physically, dispersion interaction arises from the charge density fluctuations of the subsystems, leading to weakly bound states between, for example, closed-shell partners even if they lack permanent electric moments. The importance of dispersion interaction in both chemical and biological systems cannot be overemphasized. For two subsystems at a large separation distance R, the asymptotic dispersion energy is manifested as [1]
Edisp. ≈ −
C6 , R6
Published as part of the topical collection of articles from the 17th edition of the Central European Symposium on Theoretical Chemistry (CESTC 2019) in Austria. * Á. Szabados [email protected] Á. Margócsy [email protected] 1
Doctoral School of Chemistry, Faculty of Science, ELTE Eötvös Loránd University, POB 32, Budapest 1518, Hungary
Laboratory of Theoretical Chemistry, Institute of Chemistry, Faculty of Science, ELTE Eötvös Loránd University, POB 32, Budapest 1518, Hungary
2
(1)
provided that R is not large enough for retardation effects to become noticeable. The dispersion coefficient C6 can be expressed in terms of the frequency-dependent polarizability (FDP) of each subsystem. Providing an equally accurate description of dispersion both in the equilibrium and in the asymptotic regime has remained a challenge for electronic structure methods to this day. Mean-field methods, such as Hartree–Fock (HF), cannot even qualitatively account for dispersion; such phenomena are usually introduced via correlation corrections, obtained, for example by perturbation theory (PT). Szabo and Ostlund showed [2] that a supermolecular Møller–Plesset PT2 (MP2) calculation gives rise to dispersion energy exhibiting the correct asymptotic behaviour [i.e. conforming (1)], but with C6 calculated only at the level of uncoupled HF [3]. An alternative of the supermolecule approach is the symmetryadapted perturbation theory (SAPT) of Jeziorski et al. (see Ref. [4] and references cited therein), in which the intersystem interaction is treated as perturbation. The relationship between supermolecular MP and SAPT has been investigated in detail [5]. The quality of the supermolecular approach can be improved by applying corrections more inv
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