Wang Guangming, Annaberdiyev Abdulgani, Mitas Lubos
Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202, USA.
J Chem Phys. 2020 Oct 14;153(14):144303. doi: 10.1063/5.0022814.
We present high-accuracy correlated calculations of small SiH molecular systems in both the ground and excited states. We employ quantum Monte Carlo (QMC) together with a variety of many-body wave function approaches based on basis set expansions. The calculations are carried out in a valence-only framework using recently derived correlation consistent effective core potentials. Our primary goal is to understand the fixed-node diffusion QMC errors in both the ground and excited states with single-reference trial wave functions. Using a combination of methods, we demonstrate the very high accuracy of the QMC atomization energies being within ≈0.07 eV or better when compared with essentially exact results. By employing proper choices for trial wave functions, we have found that the fixed-node QMC biases for total energies are remarkably uniform ranging between 1% and 3.5% with absolute values at most ≈0.2 eV across the systems and several types of excitations such as singlets and triplets as well as low-lying and Rydberg-like states. Our results further corroborate that Si systems, and presumably also related main group IV and V elements of the periodic table (Ge, Sn, etc), exhibit some of the lowest fixed-node biases found in valence-only electronic structure QMC calculations.
我们展示了对处于基态和激发态的小型SiH分子系统的高精度关联计算。我们采用量子蒙特卡罗（QMC）方法，并结合基于基组展开的多种多体波函数方法。计算是在仅考虑价电子的框架下进行的，使用最近推导的关联一致有效核势。我们的主要目标是利用单参考试探波函数理解基态和激发态中固定节点扩散QMC误差。通过结合多种方法，我们证明了与基本精确的结果相比，QMC原子化能的精度非常高，误差在≈0.07 eV以内或更小。通过对试探波函数进行适当选择，我们发现总能量的固定节点QMC偏差非常均匀，在整个系统以及几种类型的激发（如单重态和三重态以及低激发态和类里德堡态）中，偏差范围在1%至3.5%之间，绝对值最大约为≈0.2 eV。我们的结果进一步证实，Si系统以及周期表中可能相关的第IV和V主族元素（Ge、Sn等）在仅考虑价电子的电子结构QMC计算中表现出一些最低的固定节点偏差。
