Solvent effects on the electronic spectra: An extension of the polarizable continuum model to the ZINDO method

We present a method to evaluate absorption energies of a solvated molecule described through a semiempirical wave function. In particular, this paper extends the polarizable continuum model (PCM), in the formulation of the integral equation formalism (IEF), to the ZINDO semiempirical method. The level of theory for the interpretation of the electronic spectra is the Tamm-Dancoff approximation (TDA), using the Hartree-Fock state as reference state. Three different formulas are introduced to calculate the solute-solvent interaction potential. The most relevant formal aspects of the theory are discussed and numerical applications to the study of the transitions from the ground state to the first electronic excited state of some coumarins, of a pyridiniophenoxide betaine molecule, and of the methylene blue dye are presented.