Investigating the internally contracted multireference coupled-cluster method with perturbative triples

Ertürk M., Waigum A., Köhn A.

59th Symposium on Theoretical Chemistry, Zürich, Switzerland, 11 - 14 September 2023, pp.1

  • Publication Type: Conference Paper / Summary Text
  • City: Zürich
  • Country: Switzerland
  • Page Numbers: pp.1
  • Çanakkale Onsekiz Mart University Affiliated: Yes

Abstract

Coupled-cluster theory (CC) is valued for giving access to highly accurate and systematically improvable solutions for the electronic Schrödinger equation. The most used variant is the coupled-cluster with singles, doubles and perturbative triples (CCSD(T)). Although this method is pretty accurate, it is not able to describe chemical problems with high multireference character - like metal complexes or bond breaking. A possible extension for those is the internally contracted multireference coupled-cluster method (icMRCC). [1]\\ In this contribution we investigate the icMRCC method truncated after pair excitations with perturbative triples (icMRCCSD(T)). There, the application of the block diagonal effective fock zeroth order hamiltonian for the correction is compared to the use of the dyall zeroth order hamiltonian for such perturbative approximation is investigated. The accuracy of the different method and different approximations are tested for its application for highly accurate thermochemistry against the high-level CC methods as well as the icMRCC method using full triples (icMRCCSDT). [1] A. Köhn, J. A. Black, Y. A. Aoto, M. Hanauer, Mol. Phys., 118, e1743889 (2020).