Evaluation of Surface and Bulk Properties of Alkali Halides: A First-Principles Study on (100) and (110) Facets

Five exchange-correlation functionals (LDA, PBE, RPBE, PBE-sol, and BEEF-vdW) are studied for their accuracy in predicting bulk and surface properties of 16 alkali halides. Lattice structures, formation energies, and the surface energies of (100) and (110) facets are calculated and compared against experimental values and classical electrostatic models. While all functionals capture broad trends across the halide series, notable differences emerge in both quantitative and qualitative reliability. PBE-sol and BEEF-vdW deliver the most balanced performance across all metrics, whereas LDA and RPBE are poor performers, with larger deviations, due to over- and under-binding tendencies. Surface energy anisotropy is shown to depend on the choice of functional. The results highlight the importance of selecting appropriate methods not only for quantitative predictions but also for preserving physically meaningful descriptions of materials and surfaces. This work provides a practical benchmark for modeling ionic solids and surfaces.