Combined Hartree–Fock quantum mechanical and molecular mechanical molecular dynamics simulations of water at ambient and supercritical conditions

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Combined ab initio Hartree–Fock quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations have been carried out for water at ambient and supercritical conditions. The QM/MM coupling potential is optimized for ambient water by scaling down the original MM charges in the MM potential model. Simulation results show that the modified QM/MM coupling potential behaves well in the studied water system. The evolution of the water structure from ambient to the supercritical conditions is studied and compared to the available experimental results. Our simulation results suggest that, at supercritical conditions, the data refined from the experiment by neutron diffraction with the isotopic substitution technique probably overestimate the hydrogen bonding interactions.