Solvent effects on the electronic absorption spectrum of formamide studied by a sequential Monte Carlo/quantum mechanical approach |
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Authors: | W R Rocha V M Martins K Coutinho S Canuto |
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Institution: | 1.Núcleo de Estudos em Química Computacional, Departamento de Química, ICE, Universidade Federal de Juiz de Fora, UFJF, 36036-330 Juiz de Fora, MG, Brazil,BR;2.Universidade de Mogi das Cruzes/CCET, CP 411, 08701-970 Mogi das Cruzes, SP, Brazil,BR;3.Instituto de Física, Universidade de S?o Paulo, CP 66318, 05315-970 S?o Paulo, SP, Brazil,BR |
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Abstract: | Sequential Monte Carlo/quantum mechanical calculations are performed to study the solvent effects on the electronic absorption
spectrum of formamide (FMA) in aqueous solution, varying from hydrogen bonds to the outer solvation shells. Full quantum-mechanical
intermediate neglect of differential overlap/singly excited configuration interaction calculations are performed in the supermolecular
structures generated by the Monte Carlo simulation. The largest calculation involves the ensemble average of 75 statistically
uncorrelated quantum mechanical results obtained with the FMA solute surrounded by 150 water solvent molecules. We find that
the n → π* transition suffers a blueshift of 1,600 cm−1 upon solvation and the π → π* transition undergoes a redshift of 800 cm−1. On average, 1.5 hydrogen bonds are formed between FMA and water and these contribute with about 20% and about 30% of the
total solvation shifts of the n → π* and π → π* transitions, respectively. The autocorrelation function of the energy is used
to sample configurations from the Monte Carlo simulation, and the solvation shifts are shown to be converged values.
Received: 14 March 2002 / Accepted: 3 April 2002 / Published online: 24 June 2002 |
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Keywords: | : Formamide – QM/MM – Solvent effects – Absorption spectrum – Monte Carlo simulation |
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