A semiempirical effective Hamiltonian based approach for analyzing excited state wave functions and computing excited state absorption spectra using real-time dynamics.

We describe a new approach to extract information about an excited state wave function using a reduced orbital space molecular orbital decomposition approach for time-dependent density obtained from real-time dynamics. We also show how this information about the excited state wave function can be used to accelerate the convergence of real-time spectra and model excited state electron dynamics. We have combined this approach with our recent implementation of the real-time intermediate neglect of differential overlap for spectroscopy (INDO/S) to study the solvatochromic shift of Nile Red in acetone, ethanol, toluene and n-hexane solvents, and, for the first time, the excited state absorption spectra of coronene, 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP), zinc phthalocyanine, and nickel TPyP using a semiempirical Hamiltonian.