PNNL

Abstract

We give the details of a new partitioning scheme of the kinetic energy in molecular dynamics. The scheme utilizes instantaneous internal coordinates and atomic velocities, and at the lowest level separates the kinetic energy into solute and solvent (or bath) contributions. We illustrate its application in an analysis of the short-time dynamics of ‘cyclic’ and ‘branched’ water tetramers after an ionization event. The analysis supports the partitioning of the tetrameric systems into two subsystems, a ‘reactive trimer’ and a ‘solvent’ molecule. The partitioned kinetic energy exhibits two features, a broad peak assigned to the interaction between the two sub-systems and a sharper peak arising from the proton transfer that occurs upon ionization. It is found that the stability of the hydroxyl radical formed upon ionization is sensitive to the instantaneous configuration of the water molecules around the ionized water. Michel Dupuis was supported in part by the Division of Chemical Sciences, Office of Basic Energy Sciences, of the U.S. Department of Energy (DOE). This research was performed in part using the Molecular Science Computing Facility in the he William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at the PNNL. The EMSL is funded by DOE’s Office of Biological and Environmental Research. PNNL is operated by Battelle for DOE.