chapter
Recent improvements in the treatment of large molecular systems: modified parameters for hybrid Quantum Mechanics-Molecular Mechanics calculations.
ByY. Moreau, X. Assfeld
Pages 9

Abstract: An adapted QM:MM potential to describe the first solvation shell (or part of it) around the QM (or QM/MM) solute with the bulk effects being treated by means of a continuum model, is defined. A well- chosen set of test systems, containing functional groups of biological interest, indicate that the QM:MM interaction is larger than the QM:QM one. Since the TIP3P potential, used in this study, was developed to reproduce condensed phase systems this overestimation was expected. It is shown that a simple modification of the existing TIP3P parameters can greatly improve the accuracy of the solute-solvent interaction. The new model, named NP, proposes to increase the σ parameter and to decrease the s parameter of the Lennard-Jones potential of the oxygen atom of the water molecule only. The classical parameters of the solute (used to compute non-bonded interaction) are kept unchanged. In addition, the atomic point charges are scaled by a factor of 0.8302 reducing the dipole moment of a single molecule to a value close to the experimental gas phase measurement. The transferability and the additivity properties of the model are evaluated on the ethanol-water complexes. Furthermore, the NP parameters are used in the study of the water dimer and of the Claisen rearrangement.