半正交化基近似计算的改进

IMPROVEMENT OF APPROXIMATE CALCULATIONS BASED ON SEMIORTHOGONALIZED ORBITALS

Kashiwagi建议,在量子化学从头计算中采用半正交化基组,在电子排斥积分中忽略某些正交轨道间的重迭,同时保留核吸引积分中的类似重迭。本文建议在核吸引积分中也忽略这些微分重迭。这一改进提高了计算的精度。对仍然保留的微分重迭,在计算三、四中心积分时建议在保持电荷守恒的条件下,用较简单的轨道对之间的微分重迭代替,大大节约了计算机时。

Kashiwagi used semiorthogonalized orbitals as basis set in quantum chemicalcalculations and proposed a scheme in which two-electron integrals containing orthogonalized orbital pairs were neglected, but the same kind of one-electron integrals were reserved. We proposed in this paper that one-electron integrals containing ortho-gonalized orbital pairs should be neglected too. This improvement makes the calcu-lations more accurate, because nuclear attractive energy is approximately equal toelectron repulsive energy in a system. We use simpler orbitals to evaluate three-and four-center integrals,while keeping charge conservation. These two improvementscan save a lot of computer time in approximate ab initio calculations.