Relativistic coupled‐cluster and equation‐of‐motion coupled‐cluster methods

Abstract

The development of relativistic coupled‐cluster (CC) and equation‐of‐motion coupled‐cluster (EOM‐CC) methods is reviewed. An emphasis is placed on recent efforts to improve the computational efficiency of CC and EOM‐CC calculations with non‐perturbative treatments of spin‐orbit coupling (SO‐CC and EOM‐CC) by partially recovering spin symmetry in the formulations. Example calculations of electronic ground state as well as valence‐excited and core‐excited states for molecules containing heavy elements are presented to demonstrate the applicability and usefulness of the SO‐CC and EOM‐CC methods. Future directions for the development of the SO‐CC and EOM‐CC methods are also discussed. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods

A lower scaling four-component relativistic coupled cluster method based on natural spinors

“…Therefore, natural spinors can be determined in the same analogy as natural orbitals in the non relativistic regime: First, a DHF calculation with no pair approximation is performed which yields positive occupied and positive virtual molecular spinors only. Now the virtualvirtual block of the one-body reduced density matrix can be constructed using MBPT (2) method as:…”

“…Accurate simulation of energy and properties of heavy elements requires inclusion of both relativistic effect and electron correlation in the electronic structure calculation. The relativistic coupled cluster method, based on four or two-component Dirac-Coulomb Hamiltonian, has emerged as the method of choice for quantum chemical calculation of heavy elements due to its systematic improvable nature 1,2 . Efficient implementation of relativistic coupled cluster methods for energy, properties and excited state calculation is described in the literature [3][4][5][6][7][8] .…”

Inner-shell excitation in the YbF molecule and its impact on laser cooling

“…The Breit term has been included in the AMF scheme. We have used the CFOUR program package [29][30][31] for all calculations presented here.…”

Exact two-component Hamiltonians for relativistic quantum chemistry: Two-electron picture-change corrections made simple

“…Although it has in the meantime been employed successfully in highly sophisticated electron correlation calculations of heavy-element complexes, 48 limitations of the underlying atomic approximation to account for 2eSO PCEs have recently been pointed out in the context of zero-field splittings of first-row transition metal complexes. 49 In this paper we introduce an atomic mean-field (amfX2C) as well as an extended atomic mean-field (eamfX2C) approach within the X2C Hamiltonian framework which not only takes into account the above mentioned four main ideas in relativistic quantum chemistry but also amends them such that the resulting amfX2C and eamfX2C approaches will bridge the gap between a full molecular 4c and mmfX2C framework in a computationally efficient, yet highly accurate way.…”