Polarization interactions and boroxol ring formation in boron oxide: A molecular dynamics study

Abstract

We employ molecular dynamics (MD) simulations to study the structure of vitreous boron oxide. Although six-membered boroxol rings have been observed at fractions over 60% by various experimental techniques, simulation methods have not produced similar results. We adapt the polarization model, which includes many body polarization effects thought to stabilize such structures, for boron–oxygen interactions. This model is then used in MD simulations of boron oxide glass at various temperatures. We find a variation in the fraction of rings depending on the temperature of the system during network formation. The maximum ring fraction (∼33%) occurs when the sample is prepared at low temperatures. At these temperatures, the energy level of boron atoms in rings is 1.6% lower than the energies of boron atoms outside of rings. When higher equilibration temperatures are used, the fraction drops to 11%. Thus, two factors are relevant to boroxol ring formation in simulations of boron oxide, a model which incorporates polarization effects or their equivalent, and the appropriate manipulation of temperature history.