The Pariser-Parr-Pople model for <i>trans</i>-polyenes-Ill: Derivation of equations of motion for excited state dynamics using two-determinantal and MCSCF type electronic wave functions

Abstract

An SCF treatment for excited two-determinantal states and for multiconfiguration SCF (MCSCF), including single excitations within the framework of the semiempirical Pariser-Parr-Pople (PPP) Hamiltonian is derived. It is shown how analytical gradients of the electronic energy with respect to the geometrical variables can be calculated and the formalism for the two-determinantal state is applied to the dynamics of singlet and triplet excited Bu states of polyenes. It is shown that due to technical difficulties concerning orbital ordering the inclusion of all single excitations in the excited state wave functions via an MCSCF treatment is necessary. The use of an MCSCF procedure is important because in a CI treatment the gradients of the energy needed for the time simulations cannot be computed analytically. The necessary equations are derived.