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近20年来,作为计算量子化学主流的从头算法在预测分子几何构型和单电子性质上取得了令人信服的成功,但在能量结果上却尚差强人意。原因是分子轨道理论过分强调了电子运动的独立性而未能准确描述其相关性,导致自洽场从头算总是高估电子间的排斥能。分子精确非相对论能量与从头算给出的Hartree-Fock(以下简称H-F)能量之差称为电子相关能。后者在总能量中占的份额虽然不大(0.3—1％),但恰好与共价键能以及化学反应的势垒处于
In the past two decades, the ab initio algorithm, which is the mainstream of computational quantum chemistry, has made a convincing success in predicting molecular geometries and single electron properties, but the energy results are far from satisfactory. The reason is that molecular orbital theory overemphasizes the independence of electron motion and fails to accurately describe its correlation, resulting in that self-consistent field ab initio always overestimates the repulsion energy between electrons. The difference between the energy of a Hartree-Fock (H-F) molecule given by the exact molecular non-relativistic energy and the ab initio calculation is called the electron-related energy. Although the latter’s share of the total energy is not large (0.3-1%), the barrier just to the covalent bond energy and the chemical reaction lies in