Safari Arta A, Anderson Robert J, Manni Giovanni Li
Max-Planck-Institute for Solid State Research, 70569 Stuttgart, Germany.
J Phys Chem A. 2024 Jan 11;128(1):281-291. doi: 10.1021/acs.jpca.3c05109. Epub 2023 Dec 28.
In this work, an internally contracted stochastic complete active space second-order perturbation theory, stochastic-CASPT2, is reported. The method relies on stochastically sampled reduced density matrices (RDMs) up to rank four and contractions thereof with the generalized Fock matrix. A new protocol for calculating higher-order RDMs in full configuration interaction quantum Monte Carlo (FCIQMC) has been designed based on (1) restricting sampling of the corresponding excitations to a deterministic subspace, (2) averaging the RDMs from independent dynamics and (3) projecting them onto the closest positive semi-definite matrix. Our protocol avoids previously encountered numerical conditioning problems in the orthogonalization of the perturber overlap matrix stemming from numerical noise. The chromium dimer CASSCF(12,12)/CASPT2 binding curve is computed as a proof of concept.
在本工作中，报道了一种内部收缩的随机完全活性空间二阶微扰理论，即随机-CASPT2。该方法依赖于随机采样的秩高达四的约化密度矩阵（RDM）及其与广义福克矩阵的收缩。基于以下几点设计了一种在全组态相互作用量子蒙特卡罗（FCIQMC）中计算高阶RDM的新方案：（1）将相应激发的采样限制在一个确定性子空间；（2）对来自独立动力学的RDM进行平均；（3）将它们投影到最接近的半正定矩阵上。我们的方案避免了先前在由于数值噪声导致的微扰重叠矩阵正交化中遇到的数值条件问题。计算了铬二聚体的CASSCF(12,12)/CASPT2结合曲线作为概念验证。
