Excited States with Selected Configuration Interaction-Quantum Monte Carlo: Chemically Accurate Excitation Energies and Geometries
Excited States with Selected Configuration Interaction-Quantum Monte Carlo: Chemically Accurate Excitation Energies and Geometries
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DOI：
10.1021/acs.jctc.9b00476
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发表时间：
2019-09-01
影响因子：
5.5
通讯作者：
Filippi, Claudia
中科院分区：
文献类型：
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作者：
Dash, Monika;Feldt, Jonas;Filippi, Claudia
我们采用量子蒙特卡罗获得化学准确的垂直和绝热激发能，和平衡激发态结构的小，但具有挑战性的，甲醛和硫代甲醛分子。一个关键的成分是一个强大的协议，以获得平衡的基态和激发态Jastrow-Slater波函数在一个给定的几何形状，并保持这样一个平衡的描述，因为我们放松的结构在激发态。我们使用通过选定的配置相互作用方案，其目标是相同的二阶扰动能量校正在不同的几何形状的所有感兴趣的状态产生的行列式组件，并充分优化所得到的Jastrow-Slater波函数中的所有变分参数。重要的是，激发能以及在基态和激发态的结构参数收敛与非常紧凑的波函数，包括几千个决定因素，在一个最小的增强双c基组。这些结果已经得到在变分蒙特卡罗水平，更准确的扩散蒙特卡罗方法只产生一个小的改善绝热激发能。我们发现，匹配Jastrow-Slater波函数与类似的方差可以产生激发能量与我们的最佳估计兼容，然而，方差匹配过程需要更大的行列式展开，以达到相同的精度，它是不那么直接的结构优化过程中的激发态。
We employ quantum Monte Carlo to obtain chemically accurate vertical and adiabatic excitation energies, and equilibrium excited-state structures for the small, yet challenging, formaldehyde and thioformaldehyde molecules. A key ingredient is a robust protocol to obtain balanced ground- and excited-state Jastrow-Slater wave functions at a given geometry, and to maintain such a balanced description as we relax the structure in the excited state. We use determinantal components generated via a selected configuration interaction scheme which targets the same second-order perturbation energy correction for all states of interest at different geometries, and fully optimize all variational parameters in the resultant Jastrow-Slater wave functions. Importantly, the excitation energies as well as the structural parameters in the ground and excited states are converged with very compact wave functions comprising few thousand determinants in a minimally augmented double-c basis set. These results are obtained already at the variational Monte Carlo level, the more accurate diffusion Monte Carlo method yielding only a small improvement in the adiabatic excitation energies. We find that matching Jastrow-Slater wave functions with similar variances can yield excitation energies compatible with our best estimates; however, the variance-matching procedure requires somewhat larger determinantal expansions to achieve the same accuracy, and it is less straightforward to adapt during structural optimization in the excited state.