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arXiv 0707.3585physics.atom-phphysics.chem-ph
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原子耦合团簇计算中部分三重激发的影响

Effects of partial triple excitations in atomic coupled cluster calculations

Chiranjib Sur, Rajat K Chaudhuri

摘要:

本文用Fock空间CCSD、CCSD(T)及其幺正变体研究了高体激发在相对论CC计算中对单价电子原子和离子的影响。结果表明,CCSD(T)对碱金属原子和碱土金属离子的电离势和价电子去除能的估算相当准确,但对C Ⅱ等具有部分填充的亚壳层的原子和离子的估算结果不符合物理能级.我们进一步证明,更高的体激发效应可以更有效地纳入通过酉耦合集团理论(UCC)相比,CCSD(T)方法。

英文摘要:

In this article we study the effects of higher body excitations in the relativistic CC calculations for atoms and ions with one valence electron using Fock-space CCSD, CCSD(T) and its unitary variants. The present study demonstrates that CCSD(T) estimates the ionization potentials (IPs) and the valence electron removal energies quite accurately for alkali atoms and singly ionized alkaline earth ions, but yields unphysical energy levels for atoms and/or ions with partially filled sub-shell like C II. We further demonstrate that the higher body excitation effects can be incorporated more effectively through the unitary coupled cluster theory (UCC) compared to the CCSD(T) method.

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