Scott Mikael, Delcey Mickael G
Division of Theoretical Chemistry and Biology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
Division of Theoretical Chemistry, Department of Chemistry, Lund University, SE-221 00 Lund, Sweden.
J Chem Theory Comput. 2023 Sep 12;19(17):5924-5937. doi: 10.1021/acs.jctc.3c00317. Epub 2023 Aug 19.
We present novel developments for the highly efficient evaluation of complex linear response functions of a multiconfigurational self-consistent field (MCSCF) wave function as implemented in MultiPsi. Specifically, expressions for the direct evaluation of linear response properties at given frequencies using the complex polarization propagator (CPP) approach have been implemented, within both the Tamm-Dancoff approximation (TDA) and the random phase approximation (RPA). Purely real algebra with symmetric and antisymmetric trial vectors in a shared subspace is used wherein the linear response equations are solved. Two bottlenecks of large scale MC-CPP calculations, namely, the memory footprint and computational time, are addressed. The former is addressed by limiting the size of the subspace of trial vectors by using singular value decomposition (SVD) on either orbital or CI subspaces. The latter is addressed using an efficient parallel implementation as well as the strategy of dynamically adding linear response equations at near-convergence to neighboring roots. Furthermore, a novel methodology for decomposing MC-CPP spectra in terms of intuitive orbital excitations in an approximate fashion is presented. The performance of the code is illustrated with several numerical examples, including the X-ray spectrum of a molecule with nearly one hundred atoms. Additionally, for X-ray spectroscopy, the effect of including or excluding the core orbital in the active space on small covalent metal complexes is discussed.
我们展示了在MultiPsi中实现的用于高效评估多组态自洽场（MCSCF）波函数复杂线性响应函数的新进展。具体而言，已经实现了在Tamm-Dancoff近似（TDA）和随机相位近似（RPA）中使用复极化传播子（CPP）方法在给定频率下直接评估线性响应性质的表达式。在共享子空间中使用具有对称和反对称试矢量的纯实代数来求解线性响应方程。解决了大规模MC-CPP计算的两个瓶颈，即内存占用和计算时间。前者通过在轨道或CI子空间上使用奇异值分解（SVD）来限制试矢量子空间的大小来解决。后者通过高效的并行实现以及在接近收敛时动态地将线性响应方程添加到相邻根的策略来解决。此外，还提出了一种以近似方式根据直观的轨道激发来分解MC-CPP光谱的新方法。通过几个数值示例说明了代码的性能，包括具有近一百个原子的分子的X射线光谱。此外，对于X射线光谱学，讨论了在活性空间中包含或排除核心轨道对小共价金属配合物的影响。
