Solvation and electronic spectrum of Ni2+ ion in aqueous and ammonia solutions: A sequential Monte Carlo/TD-DFT study

A sequential Monte Carlo/Quantum Mechanics approach was used to investigate the solvent effects on d -> d transition of the Ni2+ ion in aqueous and ammonia solutions. A set of Lennard-Jones parameters were generated by modification of the UFF Force Field. The structural results obtained for the liquid structure around the Ni2+ ion are in very good agreement with the experimental findings. The water molecules in the second coordination shell interact strongly with the first shell, with hydrogen bonds of -14.6 +/- 3.3 kcal mol(-1) which is 30% stronger than in the ammonia complex. The electronic spectrum was evaluated within the TD-DFT approach on the gas phase geometry and also on the Monte Carlo generated clusters, including the long range solvent effects by means of the PCM continuum model. We show that the computed electronic transitions are all red-shifted compared with the experimental results and, the agreement with the experimental values are only qualitative. (C) 2008 Elsevier B.V. All rights reserved.