Local DFT Frequency Analysis of Alkali-Halide Clusters in Relation to Contact Melting

Gaussian/DFT Data for Ionic Crystal Cluster Models Related to Contact Melting Description This dataset contains input/output data and derived structural analysis for a series of Gaussian quantum-chemical calculations of finite ionic crystal clusters. The calculations were performed to study local structural stability, optimized geometries, vibrational modes, and coordination patterns in alkali-halide cluster models relevant to the microscopic interpretation of contact melting in ionic systems. The dataset includes optimized cluster geometries and analysis files for NaCl, LiF, NaF, KCl, and mixed NaF/LiF-type systems. The principal quantum-chemical calculations were carried out using density functional theory, mainly at the B3LYP/6-311+G(d,p) level, with geometry optimization and, where available, vibrational frequency analysis. The frequency calculations were used to distinguish confirmed local minima from structures containing imaginary vibrational modes. The data support the analysis of: optimized energies of ionic crystal clusters; first-shell cation–anion distances; coordination-number distributions; comparison with ideal finite NaCl-type crystal fragments; identification and interpretation of imaginary vibrational modes; structural differences between confirmed minima and alternative geometries; possible links between local cluster instability and contact-melting behavior in ionic systems. Confirmed minimum structures include NaCl, LiF, NaF, KCl, and mixed NaF/LiF clusters with zero imaginary frequencies. Additional files document structures with imaginary modes, which are useful for analyzing soft collective distortions and possible pathways for further geometry relaxation. This dataset accompanies a manuscript on the use of Gaussian/DFT calculations as a local quantum-chemical complement to earlier molecular-dynamics studies of contact melting in ionic crystals.