DMRG-SCF study of the singlet, triplet, and quintet states of oxo-Mn(Salen)

TL;DR

This study employs DMRG-SCF methods with CheMPS2 to analyze the electronic states of oxo-Mn(Salen), introducing an efficient procedure for selecting active spaces that enhances understanding of its electronic structure.

Contribution

The paper presents a novel approach using initial approximate DMRG calculations to determine active spaces for DMRG-SCF, reducing manual intervention and improving accuracy.

Findings

Consistent active space of 28 electrons in 22 orbitals across multiple basis sets.

New insights into the electronic structure of the quintet state.

Method simplifies active space selection for complex transition metal systems.

Abstract

We use CheMPS2, our free open-source spin-adapted implementation of the density matrix renormalization group (DMRG) [Wouters et al., Comput. Phys. Commun. 185, 1501 (2014)], to study the lowest singlet, triplet, and quintet states of the oxo-Mn(Salen) complex. We describe how an initial approximate DMRG calculation in a large active space around the Fermi level can be used to obtain a good set of starting orbitals for subsequent complete-active-space or DMRG self-consistent field (CASSCF or DMRG-SCF) calculations. This procedure mitigates the need for a localization procedure, followed by a manual selection of the active space. Per multiplicity, the same active space of 28 electrons in 22 orbitals (28e, 22o) is obtained with the 6-31G*, cc-pVDZ, and ANO-RCC-VDZP basis sets (the latter with DKH2 scalar relativistic corrections). Our calculations provide new insight into the electronic structure of the quintet.