Comparison between Gaussian and exponential charge distributions in Ewald surface potentials and fields: NaCl, aragonite, phlogopite

A comparative study has been undertaken of the employment of Gaussian and exponential charge distribution functions in calculating Coulomb potentials, energies and fields at arbitrary points due to lattice slices, using the Ewald method. The APL program SURFPOT has been developed for this purpose, for a general crystal structure with user-defined slice orientations and slice boundary configurations. Results are presented for the (111) face of NaC1, (001) and (112) faces of aragonite (CaCO₃) and (001) face of phlogopite (KM₃T₄O₁₀(OH)₂, M = divalent cation, T₄ = Si₃Al]. The convergence behaviour of the potential sums is consistently and considerably better when the Gaussian form is used.