NEW ANALYTICAL METHODS FOR CALCULATION OF THE PAIR CORRELATION FUNCTION IN TWO-COMPONENT CRYSTAL STRUCTURES.
II. NUMERICAL ACCURACY STUDY

Roman V. Chepulski and Vladirnir N. Bugaev

Dept. af Solid State Theory, Inst. for Meta1 Physics, National Academy of Sciences of Ukraine, 252680, Kiev-142, Ukraine

The numerical accuracy of the analytical approximations elaborated in part I and of a variety of other approximations advanced by now is examined, accepting the data obtained by the Monte Carlo simulation method as a standard. The approximations exhibiting the most promised for the description of crystal structure (e.g. alloys, semiconductors, magnetics, ceramics) including those with a long-range character of interactions are revealed. It is stated that, in the framework of the lattice gas model within a modified thermodynamic perturbation theory, the choice of the inverse effective radius of interactions as a small parameter of the cumulant expansion along with taking account of the contributions from only linked irreducible diagrams ensures the most quick convergence of expansion. It is demonstrated that the use of the grand canonical ensemble yields the highest numerical accuracy at the statistical- thermodynamic description within the framework of all approxmations elaborated in part I.