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本文介绍一个适用于中小有机分子的自洽场分子轨道(SCFMO)从头计算通用程序,并对各种C、H基组作了比较研究,提出一个新的最小原子轨道基组。用它试算甲烷分子的电子结构,仅用9个原子轨道(AO)和41个GTO,得到的分子总能量为E=-40.1662 hartree,比STO-KG的结果为优。例如STO-6G用9AO-54GTO得到E=-40.1011 hartree。甚至比国际通用的Gaussian-70程序所采用的4-31G双ζ基组也有改进,后者用17AO-36GTO得到E=-40.1395 hartree。此外,还在S.B.双ζ基组的基础上,在C-H键中间外加浮动键轨道,得到E=-40.1930 hartree。
In this paper, a general procedure for ab initio SCFMO calculations for small to medium sized organic molecules is presented. A comparative study of various C and H groups is presented and a new minimal atomic orbital basis set is proposed. Using it to test the electronic structure of methane molecules, using only 9 atomic orbitals (AO) and 41 GTOs, the total molecular energy obtained is E = -40.1662 hartree, which is better than that of STO-KG. For example STO-6G with 9AO-54GTO gives E = -40.1011 hartree. Even better than the 4-31G bis-zeta group used in the internationally accepted Gaussian-70 program, the latter yields E = -40.1395 hartree with the 17AO-36GTO. In addition, on the basis of the S.B. double zeta group, a floating bond orbit is added in the middle of the C-H bond to obtain E = -40.1930 hartree.