Density Operator Approach Research Articles

Excitation energies from time-dependent Hartree-Fock calculations

The time-dependent Hartree-Fock theory of molecular dynamic polarizabilities is reviewed in the context of the Dirac density operator approach. The energy ‘denominators’ are shown to vanish for external field frequencies which are solutions of an eigenvalue-equation which is the same as that arising under the random phase approximation assumptions. A perturbative approach to its solution is presented which gives good results at its lowest-order when applied to the prediction of the lowest excited singlet state of the ethylene molecule.