Sensitivity Analysis of ReaxFF Potential: The Case of Si/O System

Sensitivity analysis of the ReaxFF potential for two Si and SiO₂ systems has been carried out using the method of Morris. The goal is to identify the most important force field parameters for selected properties. Thus, a clearer physical interpretation for some of the parameters can be obtained while the ranking of the parameters per magnitude of sensitivity for each property facilitates the development of parametrizations with improved quality. The parameters related to the σ-bond and van der Waals interactions have the greatest influence on the properties of the cubic diamond Si phase. Counterintuitively, parameters which have an impact on mechanical properties, such as the ones for ππ-bonds, do not influence pressure and vice versa. For the β-cristobalite SiO₂ phase, the Si-O cross-interaction parameters have stronger effect on all properties than the Si-Si and O-O elemental ones. This dependence is attributed to the tetrahedral structure of the SiO₂ phase. Regarding the sensitivity measures, the mean of the absolute values of the elementary effect (EE) distribution correlates with the standard deviation of the EE distribution in all cases; it quantifies the sensitivity of a property on a parameter and the cross-correlation of the parameter with the other ones. The mean of the EE distribution has a poor performance and its use should be avoided. It is also argued that performing a sensitivity analysis before force field optimization might greatly enhance the efficiency of the optimization methods by considering a two-step procedure, where the most relevant parameters are optimized first.