On the example of 2-, 4- and 2,4-thiouracil we demonstrate the performance of the RASPT2/RASSCF protocol in reproducing the spectral positions and line shapes of linear absorption spectra that have been recorded in water and documented in this work. Through a QM/MM scheme coupled to a room-temperature Wigner sampling we simulate condensed phase spectra, permitting to compare our results against experiments. We discuss the sensitivity of the simulations to: a) the active space size by pushing the limits beyond the full-valence active spaces; b) the consideration of “dark” nπ ∗ -states in the state averaging; c) the flavor of RASPT2 technique; d) the basis set. The benchmarking demonstrates that full-π valence active spaces tend to red-shift the absorption band. Increasing the active space rectifies the problem and we obtain near-quantitative agreement between our experiments and calculations. We, furthermore, demonstrate that the choice of RASPT2 flavor has to be made through rigorous benchmarking.

Linear absorption spectra of solvated thiouracils resolved at the hybrid RASPT2/MM level

Borrego-Varillas R.;Cerullo G.;
2018

Abstract

On the example of 2-, 4- and 2,4-thiouracil we demonstrate the performance of the RASPT2/RASSCF protocol in reproducing the spectral positions and line shapes of linear absorption spectra that have been recorded in water and documented in this work. Through a QM/MM scheme coupled to a room-temperature Wigner sampling we simulate condensed phase spectra, permitting to compare our results against experiments. We discuss the sensitivity of the simulations to: a) the active space size by pushing the limits beyond the full-valence active spaces; b) the consideration of “dark” nπ ∗ -states in the state averaging; c) the flavor of RASPT2 technique; d) the basis set. The benchmarking demonstrates that full-π valence active spaces tend to red-shift the absorption band. Increasing the active space rectifies the problem and we obtain near-quantitative agreement between our experiments and calculations. We, furthermore, demonstrate that the choice of RASPT2 flavor has to be made through rigorous benchmarking.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11311/1123060
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