Approximate On-Top Pair Density inot One-body Functions for CAS-DFT

摘要

We have derived the new expression of the on-top pair density of CAS [2,2]by one-body functions of natura orbitals and these occupation numbers,whichwe call one-body representation of second-order density (ORSOD).The expression allows us to drastically reduce the computationla cost of complete-active-space density functional theory.Furthermoe,we define the ionic density as an approximationof ORSOD for description of potential surfaces exhibiting ionic character.We have applied these schemes for the dissociation curves of H_2 and F_2 moelcules.The relation between the ORSOD,the ion-density,and the radical-electron density that is defined in our previous work is also discussed.