Assessing and Amending Unphysical Potential Energy Surfaces in the D3 and D4 Dispersion Correction Models

The addition of dispersion corrections to density functionals is essential for accurate energy and geometry predictions. Among the most popular and computationally efficient approaches for accounting for London dispersion interactions within density functional theory are the D3 and D4 dispersion correction models. We demonstrate that these models can induce the appearance of unphysical minima on the potential energy surface (PES) when the coordination number of atoms changes. Optimizing to these artifactual structures can lead to significant errors in determining the interaction energy between two molecules and in estimating the system’s thermodynamic properties. To resolve this issue, we propose a re-parameterization of the D3 and D4 models by introducing a modified C₆^AB functional form, which explicitly depends on the specific atom pairs being considered. These new models, are termed D3-Smooth (D3S) and D4-Smooth (D4S), are designed to smooth out the PES associated with the dispersion correction. Our results demonstrate that D3S and D4S effectively eliminate unphysical local minima while maintaining the quite satisfactory accuracy of the parent D3 and D4 methods in interaction energy benchmark sets.