| We have implemented a novel formulation of ab-initio molecular dynamics in which maximally localized Wannier functions instead of delocalized Bloch states evolve on the fly during nuclear dynamics. The implementation of this scheme within Car-Parrinello (CP) molecular dynamics (MD) is presented. This scheme is further extended to include the effect of a finite homogeneous external electric field applied to the simulation cell. As an application of the former, we performed a simulation of deuterated water and calculated its infrared (IR) spectrum. We show that the oscillator strength of the translational modes, peaked around ∼185 cm-1, is anisotropic and originates from intermolecular---not intermolecular---charge fluctuations. These fluctuations are a signature of a tetrahedral hydrogen bonding environment. As an application of the latter, we performed extensive simulations of liquid water in the presence of a finite external electric field. This enables us to calculate and understand the origin of the anomalously large static dielectric constant of water. We observe that there is significant orientational correlation between a water molecule and its nearest neighbors, which arises because of the tetrahedral hydrogen bonding network in water and gives rise to its anomalously large dielectric constant. |
