Charge Distribution and Lithium Oxide Stability Modeled by Reactive Force Field.

Understanding the reactive properties of lithium and its oxides plays an important role in the modeling and design of lithium batteries. For the investigation of reasonably large structures, the use of molecular dynamics is usually the method of choice because of its calculation efficiency. The shortcoming of this approach is that the electron distribution is approximated by parameters obtained semiempirically or approximated at different levels from first-principles calculations. A novel method based on Kohn-Sham density functional theory, approximated to the second order (ACKS2), for modeling the charge distribution has recently been introduced. The method resolves two major problems from which the previous electronegativity equilibration method suffers, although some shortcomings remain. Here, we first verify the effect that the charge calculation method has on theoretical reproduction of the atomic charges obtained by the model, and then proceed to optimize the force field parameters in an attempt to alleviate the problems perceived. The newly trained ACKS2 reactive force field is validated and shown to be able to reproduce the structure and charge distribution of the lithium crystal and lithium-oxide crystal slabs enclosed by the vacuum layer.