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An Extended Interionic Potential for Alkali Halides
Author(s) -
Murti Y. V. G. S.,
Selvarajan T. V.
Publication year - 1981
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221080204
Subject(s) - van der waals force , chemistry , halide , alkali metal , ion , ionic bonding , lattice constant , london dispersion force , coupling constant , lattice (music) , formal charge , thermodynamics , physics , molecule , quantum mechanics , inorganic chemistry , organic chemistry , diffraction , acoustics
A ten‐parameter interionic potential is developed for the alkali halide crystals of rocksalt structure within the framework of the shell model for ionic crystals. This potential is an extension of the traditional Born‐Meyer form and takes into account the additional coupling between the repulsive overlap force and dispersion force. The analytical form of the proposed short‐range interaction potential is suggested by the coupled Drude oscillator model: Φ ii (r) = B ii exp (− r /σ ii ) + A ii [(1/σ ii ) 2 − 2/σ ii r ] B ii exp (− r /σ ii ) − C ii / r 6 for like ion pairs and Φ ij ( r ) = B ij exp (− r /σ ij ) for unlike ion pairs. The four like ion parameters (B ii , σ ii ) are determined by recourse to the Thomas‐Fermi electron gas model. The unlike ion repulsion parameters (B ij , σ ij ) are fixed by the requirement of consistency with the equilibrium lattice constant as well as with the dielectric data as in the shell model. The van der Waals coefficients C ii and the coupling parameters A ii are treated to be crystal‐independent. A common set of these parameters is deduced by fitting to the elastic constants over the family of sixteen crystals. The resulting van der Waals coefficients are found to be generally large for both, cations and anions. The effect of input data on the constructed potentials is studied.