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

## TL;DR

This paper introduces a new method for modeling lithium and lithium oxide charge distributions to improve battery design simulations.

## Contribution

A novel ACKS2-based reactive force field is developed and optimized to better model lithium and lithium oxide structures.

## Key findings

- The ACKS2 method improves charge distribution modeling compared to previous electronegativity equilibration methods.
- The new force field successfully reproduces lithium and lithium-oxide crystal structures with vacuum layers.
- Optimized parameters enhance the accuracy of theoretical atomic charge predictions.

## Abstract

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.