Fast evaluation of geometries and properties of excited molecules in solution: A Tamm-Dancoff model with application to 4-dimehylaminobenzene

We present a method to evaluate ab initio energy, wave function, and gradient of a solvated molecule in an electronically excited state. In particular, this paper extends the Polarizable Continuum Model (PCM) to a specific level of theory for the interpretation of the electronic spectra: configuration interaction (CI) among all singly substituted determinants using a Hartree-Fock reference state. This method, in very wide use, allows investigations of both structures and properties of electronically excited molecules through the evaluation of analytical energy derivatives with respect to various parameters. The most relevant formal aspects on the extension of the theory to solvated systems are discussed, and numerical applications to the study of geometries and one-electron properties of the low-lying excited states of 4-dimethylamino benzonitrile (DMABN) in acetonitrile solution are presented.