Lattice Energy Prediction for Complex Ionic Solids: A Generalized Simple Salt Approximation

Lattice energy is an important thermodynamic property in synthesis and application, informing the user of the stability of the solid under consideration. Methods for determining lattice energies are primarily based on lattice energy as the completion of a Born–Haber–Fajans thermochemical cycle, supplemented by mathematical molecular mechanics and quantum methods. We also note two topological regression methods. An alternative procedure is the Simple Salt Approximation (SSA) of Yoda and Flora, which involves summing the lattice energies of the constituent simple salts to yield the lattice energy of a complex salt. We here develop and implement a Generalized Simple Salt Approximation (GSSA) method that additionally uses lattice energies of solids containing ions other than those in the solid whose lattice energy is sought. Thus, GSSA considerably expands access to the lattice energies of ionic solids. Numerous examples demonstrate GSSA’s good relative agreement with both experimental data and DFT calculations of the lattice energies of a wide range of ionic solids. GSSA thus provides a simple and useful predictive method for lattice energy estimation, but absolute differences may be large for the more complex salts, which limits the practical application of the results.