激態天然軌域的特殊性質

The Special Behavior of the Natural Orbitals for Excited States

張志強(T. C. Chang) ； 包健華(C. H. Pao) ； 許貞雄(C. S. Hsue)

《化學》 43卷4期 (1985/12) Pp. 149-154

https://doi.org/10.6623/chem.1985034

摘要

過去以為使用天然軌域最經濟，且最能表現出獨立粒子的圖象。但研究具有相同對稱的兩個不閉合殼層的電子組態時，單重激態卻不適于使用天然軌域。這時候使用天然軌域只能使獨立粒子的圖象消失，而算出來的軌域單電子屬性也不具任何物理意義。為了找出在基態與激態中天然軌域有不同特性的原因，我們分析He及Be的簡單的雙組態自治場波函數的一級密度矩陣及天然軌域。我們得到的結果與用更複雜的波函數所得到的結果相符。

並列摘要

It was found that the use of natural orbitals (No) in the study of the ground states of two-electron systems can give the most natural independent particle picture and also the most economic expansion. However, the conclusion is not applicable to the singlet excited states with two orbitals of the same Symmetry. In this case the use of No is neither econmic in expansion nor meaningful in independent particle picture and the calculated one-electron properties for No are also irrelevant to any physical meaning. The novel difference between the behavior of ground and excited states is comprehensible by analysing the density matrix and Nos from the simple two configuration MCSCF type wavefunctions for He and Be atoms. The conclusion obtained are in agreement with those obtained from more sophisticate wavefunctions. So we believe that the conclusions drawn from these simple analysis are true generally.