A novel approach to the formulation of the repulsion potential of ions in ionic crystal - has been attempted. The repulsion potential is postulated to be the sum of contributions from the individual ions, these contribution3 being proportional to the coordination numbers of the ions.For the specific , exponential form of the ionic compression energy [Aexp (7 rip)] the two parameter A and p have been evaluated for 5 alkali and 4 halogen ion3 to fit the behavior of 20 alkali halide.hot only is the number of parameters (18) used in this theory less than that (26) in comparable * - '* existing ones but the fit also is better. The same parameters fit the data of the alkali haidu. ,(a) at atmospheric pressure, (b) in the pressure range 0-45 kb wherever data u available and rho (c) -. for both the low pressure NaCl and the high pressure CsCl forms when such transformations occur. The important feature in this approach IS that the.pamnetc111 evaluated for an ion in one compound in one crystal structure can be used directly for the same ion in any other crystal of any structure at0any pressure.