A local framework for calculating coupled cluster singles and doubles excitation energies (LoFEx-CCSD). (17th September 2017)

• Record Type: Journal Article
• Authors: Baudin, Pablo; Bykov, Dmytro; Liakh, Dmitry; Ettenhuber, Patrick; Kristensen, Kasper
• Is Part Of: Molecular physics. Volume 115:Number 17/18(2017)
• Page Start: 2135
• Page End: 2144
• Publication Date: 2017-09-17
• Subjects: Excitation energies -- large molecules -- coupled cluster theory -- CCSD -- local correlation; Molecules -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Molécules -- Périodiques; Chimie physique et théorique -- Périodiques; 539.6.05
• DOI: 10.1080/00268976.2017.1290836
• Languages: English
• ISSNs: 0026-8976

Abstract

ABSTRACT: The recently developed Local Framework for calculating Excitation energies (LoFEx) is extended to the coupled cluster singles and doubles (CCSD) model. In the new scheme, a standard CCSD excitation energy calculation is carried out within a reduced excitation orbital space (XOS), which is composed of localised molecular orbitals and natural transition orbitals determined from time-dependent Hartree–Fock theory. The presented algorithm uses a series of reduced second-order approximate coupled cluster singles and doubles (CC2) calculations to optimise the XOS in a black-box manner. This ensures that the requested CCSD excitation energies have been determined to a predefined accuracy compared to a conventional CCSD calculation. We present numerical LoFEx-CCSD results for a set of medium-sized organic molecules, which illustrate the black-box nature of the approach and the computational savings obtained for transitions that are local compared to the size of the molecule. In fact, for such local transitions, the LoFEx-CCSD scheme can be applied to molecular systems where a conventional CCSD implementation is intractable. Abstract :