Auxiliary-field quantum Monte Carlo calculations of the molybdenum dimer

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.

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• Computation of ground-state properties in molecular systems: back-propagation with auxiliary-field quantum Monte Carlo
• Calculation of interatomic forces and optimization of molecular geometry with auxiliary-field quantum Monte Carlo
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• Open-Shell Coupled-Cluster Valence-Bond Theory Augmented with an Independent Amplitude Approximation for Three-Pair Correlations: Application to a Model Oxygen-Evolving Complex and Single Molecular Magnet
• Accurate computations of Rashba spin-orbit coupling in interacting systems: from the Fermi gas to real materials