Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, United Kingdom.
Department of Chemistry, University of Colorado, Boulder, Colorado 80302, USA.
J Chem Phys. 2020 Oct 28;153(16):164120. doi: 10.1063/5.0023353.
We present a stochastic approach to perform strongly contracted n-electron valence state perturbation theory (SC-NEVPT), which only requires one- and two-body reduced density matrices, without introducing approximations. We use this method to perform SC-NEVPT2 for complete active space self-consistent field wave functions obtained from selected configuration interaction, although the approach is applicable to a larger class of wave functions, including those from orbital-space variational Monte Carlo. The accuracy of this approach is demonstrated for small test systems, and the scaling is investigated with the number of virtual orbitals and the molecule size. We also find the SC-NEVPT2 energy to be relatively insensitive to the quality of the reference wave function. Finally, the method is applied to the Fe(II)-porphyrin system with a (32e, 29o) active space and to the isomerization of [CuO] in a (28e, 32o) active space.
我们提出了一种随机方法来进行强收缩 n 电子价态微扰理论（SC-NEVPT），该方法仅需要一价和二价约化密度矩阵，而无需引入近似。我们使用该方法对由选定组态相互作用得到的完全活性空间自洽场波函数进行 SC-NEVPT2，尽管该方法适用于更大一类的波函数，包括那些来自轨道空间变分蒙特卡罗的波函数。我们在小测试系统中验证了该方法的准确性，并研究了该方法的扩展与虚拟轨道数量和分子大小的关系。我们还发现 SC-NEVPT2 能量对参考波函数的质量相对不敏感。最后，该方法应用于 Fe(II)-卟啉体系的（32e，29o）活性空间和[CuO]在（28e，32o）活性空间中的异构化。
