Density Matrix Renormalization Group Pair-Density Functional Theory (DMRG-PDFT): Singlet-Triplet Gaps in Polyacenes and Polyacetylenes

TL;DR

This paper introduces DMRG-PDFT, an efficient method combining DMRG and PDFT to accurately compute singlet-triplet gaps in large polyacenes and polyacetylenes, surpassing traditional methods in cost and feasibility.

Contribution

The paper presents DMRG-PDFT, a novel approach that efficiently adds dynamic correlation to DMRG wave functions for large active spaces, enabling accurate calculations beyond conventional methods.

Findings

DMRG-PDFT accurately predicts singlet-triplet gaps in polyacenes and polyacetylenes.

The method is significantly less computationally expensive than other correlation methods.

Results agree well with the most reliable literature data.

Abstract

The density matrix renormalization group (DMRG) is a powerful method to treat static correlation. Here we present an inexpensive way to add additional dynamic correlation energy to a DMRG self-consistent field (DMRG) wave function using pair-density functional theory (PDFT). We applied this new approach, called DMRG-PDFT, to study singlet-triplet gaps in polyacenes and polyacetylenes that require active spaces larger than the feasibility limit of the conventional complete active-space self-consistent field (CASSCF) method. The results match reasonably well the most reliable literature values and have only a moderate dependence on the compression of the initial DMRG wave function. Furthermore, DMRG-PDFT is significantly less expensive than other commonly applied ways of adding additional correlation to DMRG, such as DMRG followed by multireference perturbation theory or multireference configuration interaction.