Molecular dynamics simulations of the lithium coordination environment in phosphate glasses

A molecular dynamics (MD) study of the lithium ultraphosphate glass series, xLi(2)O .(1-x)P2O5 (0 less than or equal to x less than or equal to 0.5) was used to investigate the changes in the Li environment with increasing modifier concentration. The results from the MD simulations indicate that only gradual structural variations in the Li coordination environment occur as a function of modifier content. Changes in the type of oxygen coordinated to the Li are observed to correlate with the minimum in the glass transition temperature. Additionally, changes in the number of shared phosphorus vertices were seen with increasing modifier concentration, in support of recent models involving the role of the cation modifier in the extended range structure of phosphate glasses. Empirical calculations of the Li-6 NMR chemical shifts directly from the MD simulation structures are also reported and compared to recent experimental solid-state NMR results.