Multireference equation of motion coupled cluster benchmark study of magnetic model systems

Abstract

The multireference equation of motion coupled cluster (MREOM-CC) approach including spin-orbit coupling is applied to magnetic model systems FArO, FArOF and FArFOH, and compared to benchmark multireference Configuration Interaction (MRCI) approaches in the case of FArO. In the MREOM calculations, convenient high-spin states provide reference reduced density matrices, that are used to obtain a sequence of similarity transformations of the Hamiltonian. All low-lying magnetic states are obtained subsequently from a compact diagonalization of the transformed Hamiltonian. The accuracy of MREOM is shown to be comparable to MRCI+Q, but the approach is significantly more efficient for systems with a large number of electronic states. Moreover, MREOM is nearly size-consistent and this allows one to perform meaningful calculations of the strength of the magnetic coupling in the weak coupling limit.