The ROHF extension of the statistical population analysis of electron and spin densities

The authors use the first-order reduced density operator formalism to derive the statistical population analysis for ROHF wavefunctions, along the same lines as they have done before for other types of wavefunctions. In this way they find a partition of the electron density and a partition of the uncoupled spin density. The formalism is completely general and can be applied to any molecular wavefunction, whether ab initio in any level of accuracy, or semi-empirical. Numerical examples are given for systems described by an ROHF wavefunction obtained at the semi-empirical AM1 level. The comparison with UHF results is also reported.