Advantages and limitations of Kohn–Sham orbitals as single electron basis for multireference configuration interaction and multireference perturbation theory

Abstract

In the present work we study the performance of orbitals from an effective exact exchange-only optimized potential method, the localized Hartree–Fock approach, in multireference ab initio methods. In the first part local Hartree–Fock orbitals are used to describe the excited states of carbon monoxide, formaldehyde, and acetone in multireference configuration interaction calculations. The local Hartree–Fock orbitals are compared with standard Hartree–Fock orbitals, and those from a gradient corrected and a hybrid density functional. This part mainly tries to analyze possible deficiencies of the local Hartree–Fock orbitals. In the second part of this work the above-mentioned orbitals are tested in multireference perturbation theory second-order. We test to which extent known deficiencies of single state perturbation theory second-order are eliminated in multireference approaches, and then study how well local Hartree–Fock orbitals perform in multireference perturbation theory second-order computations of excited states.