Multi-Reference Epstein-Nesbet Perturbation Theory with Density Matrix Renormalization Group Reference Wavefunction

TL;DR

This paper introduces a new method combining DMRG and multi-reference ENPT2 with SCI to accurately and efficiently handle static and dynamic electron correlations in large active space systems, surpassing previous methods.

Contribution

The proposed DMRG-ENPT2 method extends applicability to very large active spaces beyond 30 orbitals, improving accuracy and efficiency in strongly correlated systems.

Findings

Successfully applied to H$_2$S with (16e, 15o) active space

Extended calculations to hexacene with (26e, 26o) active space

Performed on 2D H$_{64}$ lattice with (42e, 42o) active space

Abstract

The accurate electronic structure calculation for strongly correlated chemical systems requires an adequate description for both static and dynamic electron correlation, and is a persistent challenge for quantum chemistry. In order to account for static and dynamic electron correlations accurately and efficiently, in this work we propose a new method by integrating the density matrix renormalization group (DMRG) method and multi-reference second-order Epstein-Nesbet perturbation theory (ENPT2) with a selected configuration interaction (SCI) approximation. Compared with previous DMRG-based dynamic correlation methods, the DMRG-ENPT2 method extends the range of applicability, allowing us to efficiently calculate systems with very large active space beyond 30 orbitals. We demonstrate this by performing calculations on H$_2$S with an active space of (16e, 15o), hexacene with an active space of (26e, 26o) and 2D H$_{64}$ square lattice with an active space of (42e, 42o).