Can Density Matrix Embedding Theory with the Complete Activate Space Self-Consistent Field Solver Describe Single and Double Bond Breaking in Molecular Systems?

TL;DR

This paper introduces CAS-DMET, a novel embedding method combining density matrix embedding theory with CASSCF, to accurately describe single and double bond dissociation in molecular systems, showing promising results especially near equilibrium geometries.

Contribution

The paper develops CAS-DMET, integrating CASSCF as an impurity solver into DMET, and evaluates its effectiveness in modeling bond breaking in molecules.

Findings

CAS-DMET performs comparably to CASSCF with various active spaces.

Single embedding CAS-DMET aligns well with CASSCF at equilibrium.

Multiple embedding CAS-DMET accurately models geometries near equilibrium but less so at dissociation.

Abstract

Density matrix embedding theory (DMET) [Phys. Rev. Lett.2012, 109, 186404] has been demonstrated as an efficient wave-function-based embedding method to treat extended systems. Despite its success in many quantum lattice models, the extension of DMET to real chemical systems has been tested only on selected cases. Herein, we introduce the use of the complete active space self-consistent field (CASSCF) method as a correlated impurity solver for DMET, leading to a method called CAS-DMET. We test its performance in describing the dissociation of a H-H single bond in a H10 ring model system and an N=N double bond in azomethane (CH3-N=N-CH3) and pentyldiazene (CH3(CH2)4-N=NH). We find that the performance of CAS-DMET is comparable to CASSCF with different active space choices when single-embedding DMET corresponding to only one embedding problem for the system is used. When multiple embedding problems are used for the system, the CAS-DMET is in a good agreement with CASSCF for the geometries around the equilibrium, but not in equal agreement at bond dissociation.