An integral-factorized implementation of the driven similarity renormalization group second-order multireference perturbation theory

TL;DR

This paper presents an efficient implementation of the DSRG-MRPT2 method for multireference perturbation theory, reducing computational cost and benchmarking on naphthyne isomers to validate accuracy against coupled cluster results.

Contribution

The authors introduce a factorized integral implementation of DSRG-MRPT2 that lowers computational demands and demonstrates its effectiveness through benchmark calculations.

Findings

The implementation reduces computational cost to that of MP2.

Predicted singlet-triplet splittings align well with coupled cluster results.

Strong dependence of splittings on molecular geometries was observed.

Abstract

We report an efficient implementation of a second-order multireference perturbation theory based on the driven similarity renormalization group (DSRG-MRPT2) [C. Li and F. A. Evangelista, J. Chem. Theory Comput. 11, 2097 (2015)]. Our implementation employs factorized two-electron integrals to avoid storage of large four-index intermediates. It also exploits the block structure of the reference density matrices to reduce the computational cost to that of second-order M{\o}ller$-$Plesset perturbation theory. Our new DSRG-MRPT2 implementation is benchmarked on ten naphthyne isomers using basis sets up to quintuple-$\zeta$ quality. We find that the singlet-triplet splittings ($\Delta_\text{ST}$) of the naphthyne isomers strongly depend on the equilibrium structures. For a consistent set of geometries, the $\Delta_\text{ST}$ values predicted by the DSRG-MRPT2 are in good agreements with those computed by the reduced multireference coupled cluster theory with singles, doubles, and perturbative triples.