PNNL

Abstract

We give the details of a partitioning scheme of the kinetic energy in molecular dynamics based on instantaneous internal coordinates and atomic velocities. The scheme applied to the analysis of the short-time dynamics after ionization in ‘cyclic’ and ‘branched’ water tetramers illustrates that the tetrameric systems can be usefully partitioned into two subsystems, a ‘reactive trimer’ and a ‘solvent’ molecule. The partitioned kinetic energy exhibits a broad peak that can be assigned to the interaction between the two sub-systems, and a sharper peak arising from the proton transfer that occurs upon ionization. Comparison of the dynamics in tetramer clusters suggests that the stability of the hydroxyl radical formed upon ionization depends on the instantaneous configuration of the water molecules around the ionized water. These findings are consistent with those reported earlier for the (H2O)17 cluster. This work 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 William R. Wiley Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory (PNNL). The EMSL is funded by DOE’s Office of Biological and Environmental Research. PNNL is operated by Battelle for DOE.