A study of non-iterative triples contributions in relativistic equation-of-motion coupled-cluster calculations using an exact two-component Hamiltonian with atomic mean-field spin-orbit integrals: Application to uranyl and other heavy-element compounds

Lan Cheng

doi:10.1063/1.5113796

A study of non-iterative triples contributions in relativistic equation-of-motion coupled-cluster calculations using an exact two-component Hamiltonian with atomic mean-field spin-orbit integrals: Application to uranyl and other heavy-element compounds

J Chem Phys. 2019 Sep 14;151(10):104103. doi: 10.1063/1.5113796.

Author

Lan Cheng¹

Affiliation

¹ Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.

PMID: 31521080
DOI: 10.1063/1.5113796

Abstract

The implementation of an equation-of-motion coupled-cluster singles and doubles augmented with a noniterative triples correction [EOM-CCSD(T)(a)^*] method [D. A. Matthews and J. F. Stanton, J. Chem. Phys. 145, 124102 (2016)] with an exact two-component Hamiltonian using atomic mean-field spin-orbit integrals (X2CAMF) is reported. Benchmark calculations show that both the correction from triple excitations in the cluster operator to the similarity-transformed Hamiltonian and the contribution from triple excitations in excited-state eigenvalue equations make important contributions to computed excitation energies of molecules containing heavy elements. X2CAMF-EOM-CCSD(T)(a)^* excitation energies and excited-state properties for low-lying excited states of As₂, Sb₂, and Bi₂ are in significantly better agreement with corresponding experimental values than EOM-CCSD ones. X2CAMF-EOM-CCSD(T)(a)^* calculations have also been demonstrated to provide accurate results for excitation energies of low-lying excited states of bare uranyl ion UO₂ ²⁺, hereby resolving a long-standing debate on this topic.