CAS-DFT based on odd-electron density and radical density

We here propose new schemes of complete active space-density functional theory (CAS-DFT). It is based on the idea that the previous odd-electron density and radical density are used to express the spin-polarizability of CAS wavefunctions. We have applied these schemes to optimize geometries and to calculate the singlet–triplet energy gaps of several molecules and compare the results with those by the other methods and experiment. It was found that our schemes based on radical density give excellent results although our schemes drastically reduce the computational cost.