From hydrogen bond to bulk: Solvation analysis of the n-pi* transition of formaldehyde in water

摘要

Supermolecular calculations that treat both the solute and the solvent quantum mechanically are performed to analyze the n-pi* transition of formaldehyde in water. The liquid structures are generated by canonical (constant volume, temperature, and number of particles) (NVT) Metropolis Monte Carlo simulation. Autocorrelation function is calculated to obtain efficient ensemble average. Full quantum mechanical intermediate neglect of differential overlap/singly excited configuration interaction (INDO/CIS) calculations are then performed in the supermolecular clusters corresponding to the hydrogen bond shell and the first, second, and third solvation shells. The largest cluster, corresponding to the third solvation shell, includes 1 formaldehyde and 80 water molecules. INDO/CIS calculations are performed on a properly antisymmetric reference ground-state wave function involving all valence electrons. The results are then extrapolated to the bulk limit. The estimated Limit value for the solvatochromic shift of the n-pi* transition of formaldehyde in water, compared to gas phase, is 2200 cm(-1). (C) 2000 John Wiley & Sons, Inc. [References: 28]