A NEW BOND VALENCE BASED FORCE FIELD AND EQUATION OF STATE FOR AL, SI, O, AND H

This project follows work on the multi-pole expansion to the bond valence model (BVM), which incorporates directionalized components in the bonding model. We intend to create a new version of the BVM suitable not just for structure rationalization, but structure prediction and molecular dynamics. We have utilized the bond force models of Badger and Jonson as the basis for equating Bond Order and Bond Valence in both crystals and molecules. This model considers the bond order to be the force of the bond proportional to some standard single bond and is universal for all types of bonds: ionic, covalent, metallic etc. Utilizing a mixture of crystallographic and vibrational derived experimental structures as well as high level ab initio calculations (CCSD/cc-pVTZ) we demonstrate a force field capable of accurate bond lengths to within 0.02Å. This force field is applied to a pressure series of aluminosilicates spanning a range from 0-30GPa and is able to track the pressure isotherm as well as distinct chemical differences in the different aluminosilicate species under pressure. The ultimate goal of this work is a model with accuracies of less than or about 10 kJ/mol, a value suitable for modeling chemical reactions.