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首页> 外文期刊>The Journal of Chemical Physics >Frozen core and effective core potentials in symmetry-adapted perturbation theory
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Frozen core and effective core potentials in symmetry-adapted perturbation theory

机译：对称扰动理论中的冻结核和有效核势

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摘要

The application of the frozen-core approximation (FCA) and effective core potentials (ECPs) within symmetry-adapted perturbation theory (SAPT) has been investigated and implemented.Unlike in the case of conventional electronic-structure theories,the development of a frozen-core version of SAPT is not straightforward.In particular,the FCA realizations neglecting excitations from core orbitals and restricting all summation indices to valence orbitals only are no longer equivalent.It is shown that it is necessary in SAPT to keep some terms containing products of the valence orbitals of one monomer and the core orbitals of the other one in the exchange-energy components.When these terms are included or,equivalently,the "infinite-excitation-energy" approximation omitting only the excitations from the core orbitals is used,the accuracy of the frozen-core approximation in SAPT matches that obtained in supermolecular perturbational and coupled-cluster methods.If these terms are neglected,i.e.,within the "index-range-restriction" approximation,several exchange corrections are significantly underestimated.When ECPs are used in SAPT,the accuracy of the interaction energies is as good as in conventional supermolecular methods,provided that the residual supermolecular Hartree-Fock term is included.We have found that only some types of ECPs can be reliably used for calculations of interaction energies both in SAPT and in supermolecular approaches.For systems containing heavy atoms,both FCA and the use of ECPs lead to very significant savings of computer time.
机译：已经研究并实现了冻结核心近似（FCA）和有效核心电势（ECP）在对称自适应扰动理论（SAPT）中的应用。与传统电子结构理论不同的是， SAPT的核心版本不是一帆风顺的。尤其是，FCA实现忽略了来自核心轨道的激发并将所有求和指数限制为价轨道不再是等效的。这表明，在SAPT中，有必要保留一些包含该乘积的乘积的项。当包含交换能量时，一种单体的价轨道和另一种单体的核轨道被包括在内。或者当等效地包括“无限激发能”近似值时，仅使用来自核心轨道的激发， SAPT中冻结核近似的准确性与超分子微扰法和耦合聚类方法所获得的近似。如果忽略这些术语，即，在“指数范围限制”的近似范围内，几次交换校正都被大大低估了。当在SAPT中使用ECP时，相互作用能的精度与常规超分子方法一样，前提是剩余的超分子Hartree-Fock项为我们发现，只有某些类型的ECP可以可靠地用于计算SAPT和超分子方法中的相互作用能。对于包含重原子的系统，FCA和ECP的使用都可以大大节省计算机时间。

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