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Multi-reference Moller-Plesset theory: computational strategies for large molecules

机译：多参考Moller-Plesset理论：大分子的计算策略

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摘要

We propose computational strategies and algorithms to perform multi-reference Moller-Plesset (MR-MP2) calculations efficiently for large molecules. As zeroth-order reference we employ restricted configuration interaction wave functions expressed in terms of an active space of Hartree-Fock one-particle functions (RAS-CI). To accelerate the convergence of the perturbation expansion and to keep the zeroth-order spaces as small as possible (i.e. Dim < 1000) we use improved (average) virtual orbitals. The length of the first-order space (single and double excitations with respect to all reference configurations) is reduced by selecting the most important configurations from the full space based on the magnitude of their H-0 diagonal matrix element. The two-electron integrals in the MO basis are calculated semi-directly with the resolution of the identity (RI) method which avoids computationally demanding 4-index transformations. The errors introduced by the approximations can systematically be reduced and are found to be insignificant in applications to chemical problems. As examples we present MR-MP2 results for excitation and reaction energies of molecules for which single-reference perturbation theory is not adequate. With our approach, investigation of systems as large as porphin or C-60 are possible on low-cost personal computers. [References: 35]
机译：我们提出了计算策略和算法，可以对大分子有效地执行多参考Moller-Plesset（MR-MP2）计算。作为零阶参考，我们采用了以Hartree-Fock单粒子函数（RAS-CI）的活动空间表示的受限配置相互作用波函数。为了加快摄动展开的收敛速度并保持零阶空间尽可能小（即Dim <1000），我们使用了改进的（平均）虚拟轨道。通过基于H-0对角矩阵元素的大小从整个空间中选择最重要的配置，可以减少一阶空间的长度（相对于所有参考配置而言是单激励和双激励）。以MO为基础的半电子式，使用恒等（RI）方法的分辨率进行半直接计算，该方法避免了计算上要求较高的4指数转换。由近似值引入的误差可以系统地减小，并且发现在化学问题的应用中不重要。作为示例，我们介绍了单参考微扰理论不足的分子的激发和反应能的MR-MP2结果。使用我们的方法，可以在低成本的个人计算机上研究像海豚或C-60一样大的系统。 [参考：35]

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