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 ¹B_u 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.