AB-INITIO LIQUID WATER

An ab initio molecular dynamics simulation of liquid water has been pe rformed using density functional theory in the Kohn-Sham formulation a nd a plane wave basis set to determine the electronic structure and th e forces at each time step. For an accurate description of the hydroge n bonding in the liquid, it was necessary to extend the exchange funct ional with a term that depends on the gradient of the electron density . A further important technical detail is that supersoft pseudopotenti als were used to treat the valence orbitals of the oxygen atoms in a p lane wave expansion. The structural and dynamical properties of the li quid were found to be in good agreement with experiment. The ab initio molecular dynamics also yields information on the electronic structur e. The electronic feature of special interest is the lowest unoccupied molecular orbital (LUMO) of the liquid which is the state occupied by a thermalized excess electron in the conductive state. The main resul t of calculating the liquid LUMO is that it is a delocalized state dis tributed over interstitial space between the molecules with a signific ant admixture of the sigma orbitals of the individual water molecules .