N-electron valence state perturbation theory based on a density matrix renormalization group reference function, with applications to the chromium dimer and poly-p-phenylene vinylene oligomer

TL;DR

This paper introduces a combined DMRG and NEVPT2 method to accurately compute electronic structures of complex molecules, effectively handling static and dynamic correlations, demonstrated on the chromium dimer and PPV oligomer.

Contribution

It develops a DMRG-SC-NEVPT2 approach that efficiently computes high order density matrices, enabling accurate treatment of large active spaces in challenging molecules.

Findings

Accurate potential energy curve for chromium dimer at basis set limit.

Reliable excitation energies for PPV trimer.

Demonstrates effectiveness of the method on complex transition metal and conjugated systems.

Abstract

The strongly-contracted variant of second order N -electron valence state perturbation theory (NEVPT2) is an efficient perturbative method to treat dynamic correlation without the problems of intruder states or level shifts, while the density matrix renormalization group (DMRG) provides the capability to tackle static correlation in large active spaces. We present a combination of the DMRG and strongly-contracted NEVPT2 (DMRG-SC-NEVPT2) that uses an efficient algorithm to compute high order reduced density matrices from DMRG wave functions. The capabilities of DMRG-SC-NEVPT2 are demonstrated on calculations of the chromium dimer potential energy curve at the basis set limit, and the excitation energies of poly-p-phenylene vinylene trimer (PPV(n=3)).