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光电子能谱的理论研究已成为量子化学工作者感兴趣的课题,其首要任务是垂直电离势(VIP)的精确计算。根据Koopmans定理,可由分子轨道能得到VIP。然而Koopmans理论是一种粗略的近似,(N-1)-电子体系中分子轨道的调整和N-电子体系与(N-1)-电子体系不等的相关能使Koopmans VIP值存在着两类误差。VIP的E_(△SCF)方法计算虽然考虑了轨道调整这一因素,但需要对N-电子体系和(N-1)-电子体系进行两次SCF计算。理论上讲,E_(ACI)计算能给出正确结果,但计算费用十分昂贵。
The theoretical study of photoelectron spectroscopy has become an issue of interest to quantum chemical workers. Its primary task is the accurate calculation of the vertical ionization potential (VIP). According to Koopmans theorem, VIP can be obtained from molecular orbitals. However, the Koopmans theory is a rough approximation. The adjustment of molecular orbitals in (N-1) -electron systems and the unequal correlation between N-electron systems and (N-1) error. VIP’s E_ (△ SCF) method Although the factor of orbit adjustment is taken into consideration, it is necessary to make two SCF calculations for N-electron system and (N-1) -electron system. In theory, E_ (ACI) calculation can give the correct result, but the computational cost is very expensive.