Integrated computational approaches for spectroscopic studies of molecular systems in the gas phase and in solution: pyrimidine as a test case Malgorzata BiczyskoJulien BloinoGiuseppe BrancatoIvo CacelliChiara Cappelli • Alessandro FerrettiAlessandro LamiSusanna MontiAlfonso PedoneGiacomo Prampolini • Cristina PuzzariniFabrizio SantoroFabio TraniGiovanni Villani

An integrated computational approach built on quantum mechanical (QM) methods, purposely tailored inter- and intra-molecular force fields and continuum sol- vent models combined with time-independent and time- dependent schemes to account for nuclear motion effects is applied to the spectroscopic investigation of pyrimidine in the gas phase as well as in aqueous and CCl4 solutions. Accurate post-Hartree-Fock methodologies are employed to compute molecular structure, harmonic vibrational fre- quencies, energies and oscillator strengths for electronic transitions in order to validate the accuracy of approaches rooted into density functional theory with emphasis also on hybrid QM/QM 0 models. Within the time-independent approaches, IR spectra are computed including anharmo- nicities through perturbative corrections while UV-vis line-shapes are simulated accounting for the vibrational structure; in both cases, the environmental effects are described by continuum models. The effects of confor- mational flexibility, including solvent dynamics, are described through time-dependent models based on pur- posely DFT-tailored force fields applied to molecular dynamics simulations and on QM computations of spec- troscopic properties. Such procedures are exploited to Dedicated to Professor Vincenzo Barone and published as part of the special collection of articles celebrating his 60th birthday.