ABSTRACT
First-principles computations are paramount for understanding of molecular properties. Low-resolution spectroscopic studies are typical applications where such modeling can be helpful, allowing to find a link between the spectral signal and the structure and dynamics of investigated systems. Because of computer limits, molecular environment can be involved in the computations only approximately. We investigated the approximations that have to be done for reasonable simulations of vibrational and electronic molecular excited states. For the vibrations, the molecules see the environment mainly as an electrostatic perturbation. This makes the modeling easier, as the surrounding water molecules, for example, can be substituted by point charges or a dielectric continuum. For the electronic states, the electrostatic influence is important, too. However, direct participation of solvent molecular orbitals in the electronic excitations has to be additionally taken into account. Only when the solvent is treated properly, structure and dynamics of model peptides can be deduced from Raman optical activity and electronic circular dichroism spectra.
