Molecular dynamics study of electron gas models for liquid water

The frozen density electron gas model proposed by Gordon and Kim for rare gas systems has been implemented in a molecular dynamics code. This code has been applied to investigate various options for extending this scheme to inter-molecular interactions in liquid water. We have compared a number of gradient corrections to the Thomas-Fermi kinetic energy. We also explored a more empirical approach based on adaptation of the frozen molecular electron density to the condensed phase environment. Consistent with experience from force field methods, enhancement of the molecular dipole moment proved to be necessary to reproduce the properties of the liquid. The best models we investigated are a gradient corrected expansion of the simple local density Hamiltonian applied in the original Gordon and Kim model. In addition, these models observed a modified molecular electron density carrying the same dipole moment of 2.95 D as has been observed by recent ab initio molecular dynamics studies based on fully self-consistent Kohn-Sham methods. Possible implications of this finding for force field models are discussed.