Auxiliary-field quantum Monte Carlo calculations of the molybdenum dimer

TL;DR

This paper employs advanced auxiliary-field quantum Monte Carlo methods to accurately compute the electronic states of the molybdenum dimer, achieving results that align well with experimental data and providing insights into transition metal electron correlation.

Contribution

The study introduces high-level AFQMC benchmarks for Mo2, including extrapolation to the complete basis set limit, addressing previous computational challenges with transition metal dimers.

Findings

Excellent agreement with experimental spectroscopic constants.

Comparison of correlation effects in Cr2 and Mo2.

Successful application of AFQMC to transition metal dimers.

Abstract

Chemical accuracy is difficult to achieve for systems with transition metal atoms. Third row transition metal atoms are particularly challenging due to strong electron-electron correlation in localized d-orbitals. The Cr2 molecule is an outstanding example, which we previously treated with highly accurate auxiliary-field quantum Monte Carlo (AFQMC) calculations [Purwanto et al., J. Chem. Phys. 142, 064302 (2015)]. Somewhat surprisingly, computational description of the isoelectronic Mo2 dimer has also, to date, been scattered and less than satisfactory. We present high-level theoretical benchmarks of the Mo2 singlet ground state ($X ^1\Sigma_g^+$) and first triplet excited state ($a ^3\Sigma_u^+$), using the phaseless AFQMC calculations. Extrapolation to the complete basis set limit is performed. Excellent agreement with experimental spectroscopic constants is obtained. We also present a comparison of the correlation effects in Cr2 and Mo2.