Al-Saidi W A, Krakauer Henry, Zhang Shiwei
Department of Physics, College of William and Mary, Williamsburg, Virginia 23187-8795, USA.
J Chem Phys. 2007 May 21;126(19):194105. doi: 10.1063/1.2735296.
The authors present phaseless auxiliary-field (AF) quantum Monte Carlo (QMC) calculations of the ground states of some hydrogen-bonded systems. These systems were selected to test and benchmark different aspects of the new phaseless AF QMC method. They include the transition state of H+H(2) near the equilibrium geometry and in the van der Walls limit, as well as the H(2)O, OH, and H(2)O(2) molecules. Most of these systems present significant challenges for traditional independent-particle electronic structure approaches, and many also have exact results available. The phaseless AF QMC method is used either with a plane wave basis with pseudopotentials or with all-electron Gaussian basis sets. For some systems, calculations are done with both to compare and characterize the performance of AF QMC under different basis sets and different Hubbard-Stratonovich decompositions. Excellent results are obtained using as input single Slater determinant wave functions taken from independent-particle calculations. Comparisons of the Gaussian based AF QMC results with exact full configuration interaction show that the errors from controlling the phase problem with the phaseless approximation are small. At the large basis-size limit, the AF QMC results using both types of basis sets are in good agreement with each other and with experimental values.
作者展示了对一些氢键体系基态的无相辅助场（AF）量子蒙特卡罗（QMC）计算。选择这些体系是为了测试和基准化新的无相AF QMC方法的不同方面。它们包括处于平衡几何结构附近以及范德华极限下的H+H₂的过渡态，还有H₂O、OH和H₂O₂分子。这些体系中的大多数对传统独立粒子电子结构方法构成了重大挑战，而且许多体系也有精确结果可供参考。无相AF QMC方法既可以与带有赝势的平面波基组一起使用，也可以与全电子高斯基组一起使用。对于一些体系，两种方法都进行了计算，以比较和表征AF QMC在不同基组和不同哈伯德 - 斯特拉托诺维奇分解下的性能。使用从独立粒子计算中获取的单斯莱特行列式波函数作为输入，得到了出色的结果。基于高斯的AF QMC结果与精确的全组态相互作用的比较表明，通过无相近似控制相位问题产生的误差很小。在大基组规模极限下，使用两种基组的AF QMC结果彼此之间以及与实验值都吻合得很好。
