(633b) First Principles Simulations of Siliceous Melts and Aggregating Vapors

First principles simulations are applied to investigate two systems: (i) siliceous melts where unusual coordination environments are present at high temperature and high pressure, and (ii) the superheated vapor phase of hydrogen fluoride where clustering is prevalent at lower temperatures.  Molecular dynamics simulations in the isobaric-isothermal ensemble using the CP2K software are carried out to explore thermodynamic, structural and transport properties of hydrous silica and silicate melts as function of temperature and pressure.  These simulations use Kohn-Sham density functional theory with the BLYP functional and the Gaussian plane wave approach that allows for efficient computation of the electronic energy for condensed phases.  Analysis of the simulation trajectories for hydrous silica and silicate melts yields a wealth of information on the effects of water concentration on the volumetric and structural properties and on speciation.  Aggregation-volume-bias Monte Carlo simulations in the isobaric-isothermal ensemble using the MCCCS-MN software are carried out to explore thermodynamic and structural properties of the superheated hydrogen fluoride vapor phase.  Given the relatively low densities of this system, the electrostatically embedded many-body approach is used that makes is feasible to compute the electronic energy either using KS-DFT or the MP2 approach.