Accurate many-body electronic structure near the basis set limit: application to the chromium dimer

TL;DR

The paper introduces a novel computational method combining variational and perturbative techniques to accurately determine electronic energies near the basis set limit, demonstrated on the challenging chromium dimer molecule.

Contribution

A new semistochastic approach efficiently computes near-exact energies for complex correlated systems by focusing on important basis states and applying perturbative corrections.

Findings

Successfully computed a near-exact potential energy curve for the chromium dimer.

Method achieves high accuracy close to the basis set limit.

Demonstrates efficiency in handling large Hilbert spaces.

Abstract

We describe a method for computing near-exact energies for correlated systems with large Hilbert spaces. The method efficiently identifies the most important basis states (Slater determinants) and performs a variational calculation in the subspace spanned by these determinants. A semistochastic approach is then used to add a perturbative correction to the variational energy to compute the total energy. The size of the variational space is progressively increased until the total energy converges to within the desired tolerance. We demonstrate the power of the method by computing a near-exact potential energy curve (PEC) for a very challenging molecule -- the chromium dimer.