New Force-Field for Organosilicon Molecules in the Liquid Phase

In this paper, wepresent a new molecular model that can accuratelypredict thermodynamic liquid state and phase-change properties fororganosilicon molecules including several functional groups (alkylsilane,alkoxysilane, siloxane, and silanol). These molecules are of greatimportance in geological processes, biological systems, and materialscience, yet no force field currently exists that is widely applicableto organosilicates. The model is parametrized according to the recentPolarization-Consistent Approach (PolCA), which allows for polarizationeffects to be incorporated into a nonpolarizable model through post facto correction terms and is therefore consistentwith previous parametrizations of the PolCA force field. Alkyl groupsare described by the United-Atom approach, bond and angle parameterswere taken from previous literature studies, dihedral parameters werefitted to new quantum chemical energy profiles, point charges werecalculated from quantum chemical optimizations in a continuum solvent,and Lennard-Jones dispersion/repulsion parameters were fitted to matchthe density and enthalpy of vaporization of a small number of selectedcompounds. Extensive validation efforts were carried out, after carefulcollection and curation of experimental data for organosilicates.Overall, the model performed quite well for the density, enthalpyof vaporization, dielectric constant, and self-diffusion coefficient,but it slightly overestimated the magnitude of self-solvation freeenergies. The modular and transferable nature of the PolCA force fieldallows for further extensions to other types of silicon-containingcompounds.