A semi-empirical approach for the cohesive energy of the Alkali Halides

Many formulae are available for the cohesive energy of the alkali halides. These have many terms and the predictions of most of these are not very accurate. We give a semi-empirical formula for the cohesive energy of the alkali halides, except the Cs halides because three of these differ in structure from the other members of the alkali halides. Our formula consists of only three terms. It is more accurate than the seven formulae presented here, yet it is the simplest of these. If only the first term is taken, its prediction should be sufficient for most ordinary purposes. More importantly, the treatment gives an insight into the physics of the ionic compounds. However, that does not, in any way, diminish the value of the microscopic treatments. For the purpose of comparing the different formulae, a Χ² is constructed on the plausible basis that the cohesive energy data may be inaccurate upto the extent of 1%. However, the Χ² should still serve as a reliable index for comparison if the inaccuracy is different from 1%.