Validation of formulation of interatomic potential model results by density functional theory: Accuracy hierarchy and systematic bias in binding energy predictions

Binding energy is an important parameter that governs the structural characteristics, lattice behavior, and thermophysical properties of ionic solids. In this investigation, the binding energies of alkali halides are rigorously determined using analytical interatomic potential equations and first-principles density functional theory (DFT), and the results are compared with experimental data. Binding energy closed-form expressions are obtained from Born–Mayer, Varshni–Shukla, Gaussian, and Logarithmic (L5) potential functions under the conditions of equilibrium and stability. We discuss in depth the effects of equilibrium intermolecular separation and force constant on binding energy. Calculations of DFT for representative alkali halides of the rocksalt structure based on the generalized gradient approximation are taken to give an intrinsic quantum-mechanical reference. The binding energy and equilibrium separation are inversely related, indicating the importance of Coulombic interactions in ionic bonding. Among the analytical models, the Logarithmic (L5) potential shows the best agreement with experimental results, whereas the Born–Mayer and Varshni–Shukla models are more biased toward overestimation, and the Gaussian model is biased toward underestimating the binding energies. DFT results closely model the experimental binding energies and can serve as a reference for evaluating analytical models. Through the joint analytical–DFT approach, it can elucidate the mechanisms by which intermolecular separation, lattice stiffness, anharmonicity, and electronic effects govern the binding energy of ionic solids.