Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA.
Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
J Chem Phys. 2023 Apr 14;158(14):140901. doi: 10.1063/5.0134009.
Approximate solutions to the ab initio electronic structure problem have been a focus of theoretical and computational chemistry research for much of the past century, with the goal of predicting relevant energy differences to within "chemical accuracy" (1 kcal/mol). For small organic molecules, or in general, for weakly correlated main group chemistry, a hierarchy of single-reference wave function methods has been rigorously established, spanning perturbation theory and the coupled cluster (CC) formalism. For these systems, CC with singles, doubles, and perturbative triples is known to achieve chemical accuracy, albeit at O(N) computational cost. In addition, a hierarchy of density functional approximations of increasing formal sophistication, known as Jacob's ladder, has been shown to systematically reduce average errors over large datasets representing weakly correlated chemistry. However, the accuracy of such computational models is less clear in the increasingly important frontiers of chemical space including transition metals and f-block compounds, in which strong correlation can play an important role in reactivity. A stochastic method, phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC), has been shown to be capable of producing chemically accurate predictions even for challenging molecular systems beyond the main group, with relatively low O(N - N) cost and near-perfect parallel efficiency. Herein, we present our perspectives on the past, present, and future of the ph-AFQMC method. We focus on its potential in transition metal quantum chemistry to be a highly accurate, systematically improvable method that can reliably probe strongly correlated systems in biology and chemical catalysis and provide reference thermochemical values (for future development of density functionals or interatomic potentials) when experiments are either noisy or absent. Finally, we discuss the present limitations of the method and where we expect near-term development to be most fruitful.
从头算电子结构问题的近似解一直是理论和计算化学研究的重点，在过去的一个世纪中，其目标是预测相关能量差异达到“化学精度”（1 kcal/mol）。对于小分子，或者一般来说，对于弱关联的主族化学，已经严格建立了一系列单参考波函数方法的层次结构，涵盖了微扰理论和耦合簇（CC）形式。对于这些系统，已知 CC 与单重态、双重态和微扰三重态相结合可以达到化学精度，尽管计算成本为 O(N)。此外，随着形式的复杂性增加，密度泛函近似的层次结构，即雅各布天梯，已被证明可以系统地减少代表弱关联化学的大数据集的平均误差。然而，在化学空间越来越重要的前沿领域，包括过渡金属和 f 区化合物，这些计算模型的准确性就不太清楚了，在这些领域中，强相关性可以在反应性中发挥重要作用。一种随机方法，无相位辅助场量子蒙特卡罗（ph-AFQMC），已被证明即使对于超出主族的具有挑战性的分子系统，也能够产生化学精度的预测，其相对 O(N-N)成本较低，且近乎完美的并行效率。在此，我们提出了对 ph-AFQMC 方法过去、现在和未来的看法。我们重点介绍了它在过渡金属量子化学中的潜力，作为一种高度准确、系统可改进的方法，可以可靠地探测生物学和化学催化中的强关联系统，并在实验存在噪声或不存在时提供参考热化学值（用于密度泛函或原子间势的未来发展）。最后，我们讨论了该方法的当前限制以及我们预计近期发展最有成效的领域。
