An Auxiliary-Field Quantum Monte Carlo Study of the Chromium Dimer

TL;DR

This paper employs advanced quantum Monte Carlo methods to accurately compute the potential energy curve and properties of the challenging chromium dimer, achieving results that closely match experimental data.

Contribution

It introduces a near-exact AFQMC approach combining unconstrained and extrapolation techniques to study the Cr2 molecule with high accuracy.

Findings

Final PEC and spectroscopic constants agree well with experiments

Elimination of finite-basis errors through extrapolation

Demonstrates AFQMC's effectiveness for strongly correlated systems

Abstract

The chromium dimer (Cr2) presents an outstanding challenge for many-body electronic structure methods. Its complicated nature of binding, with a formal sextuple bond and an unusual potential energy curve, is emblematic of the competing tendencies and delicate balance found in many strongly correlated materials. We present a near-exact calculation of the potential energy curve (PEC) and ground state properties of Cr2, using the auxiliary-field quantum Monte Carlo (AFQMC) method. Unconstrained, exact AFQMC calculations are first carried out for a medium-sized but realistic basis set. Elimination of the remaining finite-basis errors and extrapolation to the complete basis set (CBS) limit is then achieved with a combination of phaseless and exact AFQMC calculations. Final results for the PEC and spectroscopic constants are in excellent agreement with experiment.