Purwanto Wirawan, Zhang Shiwei, Krakauer Henry
Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
J Chem Phys. 2016 Jun 28;144(24):244306. doi: 10.1063/1.4954245.
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.
对于含有过渡金属原子的体系而言，实现化学精度颇具难度。由于局域d轨道中存在强电子-电子关联，第三周期过渡金属原子尤其具有挑战性。Cr₂分子就是一个典型例子，我们之前曾采用高精度的辅助场量子蒙特卡罗（AFQMC）计算对其进行处理[W. Purwanto等人，《化学物理杂志》142, 064302 (2015)]。颇为出人意料的是，迄今为止，等电子体Mo₂二聚体的计算描述也较为零散且不尽人意。我们运用无相位AFQMC计算，给出了Mo₂单重基态（X(1)Σg(+)）和第一重三重激发态（a(3)Σu(+)）的高水平理论基准。进行了外推至完备基组极限的操作。获得了与实验光谱常数的极佳吻合。我们还对Cr₂和Mo₂中的关联效应进行了比较。
