Condensed Matter Physics, 2018, vol. 21, No. 4, 43501
DOI:10.5488/CMP.21.43501           arXiv:1812.08536

Title: Cluster expansion for the description of condensed state: crystalline cell approach
  G.S. Bokun (Belarusian State Technological University, 13a Sverdlov St., 220006 Minsk, Belarus) ,
  M.F. Holovko (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii St., 79011 Lviv, Ukraine)

A well-known cluster expansion, which leads to virial expansion for the free energy of low density systems, is modified in such a way that it becomes applicable to the description of condensed state of matter. To this end, the averaging of individual clusters over the states of an ideal gas is replaced by the averaging over the states of a non-correlated crystal using single-particle cell potentials. As a result, we arrive at the expansion of the partition function in correlations on the basis of single-particle functions corresponding to the multiplicative approximation. The cell potentials defining these functions are found from the condition of the minimum of the remainder in the constructed decomposition.

Key words: lattice models, cluster expansions, single-particle cell potential, free energy
PACS: 5.20.-y, 61.72jd, 64.30.-t, 65.40.-b

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