Kollmar Christian, Sivalingam Kantharuban, Helmich-Paris Benjamin, Angeli Celestino, Neese Frank
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany.
Dipartimento di Scienze Chimiche e Farmaceutiche, Università di Ferrara, Via Borsari 46, I-44100 Ferrara, Italy.
J Comput Chem. 2019 May 30;40(14):1463-1470. doi: 10.1002/jcc.25801. Epub 2019 Feb 23.
A perturbation theory-based algorithm for the iterative orbital update in complete active space self-consistent-field (CASSCF) calculations is presented. Following Angeli et al. (J. Chem. Phys. 2002, 117, 10525), the first-order contribution of singly excited configurations to the CASSCF wave function is evaluated using the Dyall Hamiltonian for the determination of a zeroth-order Hamiltonian. These authors employ an iterative diagonalization of the first-order density matrix including the first-order correction arising from single excitations, whereas the present approach uses the single-excitation amplitudes directly for the construction of the exponential of an anti-Hermitian matrix resulting in a unitary matrix which can be used for the orbital update. At convergence, the single-excitation amplitudes vanish as a consequence of the generalized Brillouin's theorem. It is shown that this approach in combination with direct inversion of the iterative subspace (DIIS) leads to very rapid convergence of the CASSCF iteration procedure. © 2019 Wiley Periodicals, Inc.
提出了一种基于微扰理论的算法，用于完全活性空间自洽场（CASSCF）计算中的迭代轨道更新。按照安杰利等人（《化学物理杂志》，2002年，第117卷，第10525页）的方法，使用戴尔哈密顿量来确定零阶哈密顿量，从而评估单激发组态对CASSCF波函数的一阶贡献。这些作者采用一阶密度矩阵的迭代对角化，其中包括单激发产生的一阶修正，而本文方法直接使用单激发振幅来构建反厄米矩阵的指数，从而得到一个可用于轨道更新的酉矩阵。在收敛时，由于广义布里渊定理，单激发振幅消失。结果表明，该方法与迭代子空间直接反演（DIIS）相结合，可使CASSCF迭代过程非常快速地收敛。©2019威利期刊公司。
