Ab initiocalculations of static lattice properties for NaCl and a test of the Decker equation of state

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Abstract
Calculations of the equilibrium volume and bulk modulus at the equilibrium volume are made for Gordon-Kim based theories of NaCl and used in the Decker approach for calculating the equation of state. Generally the resultant ‘‘Decker equation of state’’ is in excellent agreement with the exact calculations. However, for one theory a 9% discrepancy is obtained for the highest B1-phase pressures, i.e., p=30 GPa. Results of the application of this analysis to recent linear augmented-plane-wave calculations, which make no approximation beyond the local-density approximation, are also presented and give added support to the validity of the Decker procedure. It is also shown that a five-parameter Birch formula, where tested rigorously, is an excellent representation of crystal-energy versus volume calculations. Finally, results of the second pressure derivative of the bulk modulus, evaluated at zero pressure, are found to be in fair agreement with a recent experimental determination.