title: 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 [W. 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)Σg (+)) and first triplet excited state (a(3)Σu (+)), 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.
authors.affiliation: Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
authors.forename: Wirawan
authors.initials: W
authors.lastname: Purwanto
authors.affiliation: Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
authors.forename: Shiwei
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Krakauer