Ground-state density-matrix algorithm for excited-state adiabatic surfaces: application to polyenes

A low-cost method for computing excited-state adiabatic surfaces, which totally avoids the calculation of the excited-state many-electron wavefunctions, and scales favorably with molecular size is proposed. The technique combines standard ground-state calculations with a time-dependent density-matrix calculation of vertical optical excitations, using the ground-state single-electron density matrix as an input. Several surfaces are generated simultaneously. The structure and vibrational frequencies of the 1Bu state of hexatriene and octatetraene are calculated using this method. The computed sign of the excited-state equilibrium displacements facilitates rapid analysis of resonance Raman measurements.