A perturbation theory calculation of the exchange energy of the HeH++molecular ion

摘要

The problem of a heteronuclear one electron molecule with different nuclear chargesz1andz2has been analyzed by a perturbation treatment. Starting from a homonuclear system in which each nucleus has the average charge (z1+z2)/2, the plusmn;(z1minus;z2)/2 difference charges with opposing signs at the two nuclei are used as a perturbation. For HeH++secondhyphen;order perturbation calculations of the ground and first excited states are in very good agreement with exact calculations. The model predicts the correct behavior forRrarr;0 and forRrarr;infin; when there is no crossing of the energy levels. The electronic energies of ten lowhyphen;lying excited states are also in good agreement with the exact numerical results. This analysis clarifies the role of exchange in a simple heteronuclear system.