Annotation: The purpose of work is development of the computer program of design of cluster structure of fusions of simple metals with the crystalline grate of type of body centered cubic (BCC) for comparison with experimental data of X - raying. For this purpose methods are worked out:
1. Calculation of coordination numbers on a cluster for their subsequent middling according to sample and comparison (approximations) with the experimental radial function of distribution of atoms (RFDA). Thus the choice of form of cluster was carried out in accordance with principle of Curie-Woulf and Brave - about a minimum of superficial energy of crystal, being in an equilibrium with the liquid, and that a crystal is limited to the atomic planes with the maximal closeness of atoms. For BCC of grate clusters correspond them in a form: bipyramids, prisms, threepyramids, moreover first from named corresponds most ratio of volume toward the area of surface, i.e. she is most credible.
2. For the forms of clusters indicated higher the discrete functions of form and their continuous analogues were certain in different directions of translations.
3. To the finding functions were certain Fourier- characters (intensities) for description of types of diffraction peaks for the case of bipyramids.
The use of finding dependences is work out the computer program of design of cluster structure, which consisted in approximation of experimental data of X - raying researches of fusions of alkaline metals a theoretical model.The results of approximation it is been: determination of mean value of coordination number, middle interatomic distance, optimal clustersize, middle distance between clusters. Calculations is executed for many alkaline metals in the wide interval of temperatures. Data for a rubidium at the temperature of 513К have next values: middle interatomic distance - 5,755 Å, optimal clustersize - 12,756 Å, middle coordination number - 1,325, middle c distance between clusters - 0,518 Å.
Key word: co-ordinating numbers, optimal clustersize.