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The work is aimed at studying the influence of correlation effects on the interaction energy of two-dimensional (2D) polarons. The two-center configuration of 2D bipolaron corresponds to a shallow secondary minimum, which occurs when only the correlations associated with the permutation symmetry of the system are taken into account. The correlations associated with the direct dependence of the electron wave function on the distance between electrons lead to stabilization of the one-center configuration, and the secondary minimum corresponding to the two-center configuration disappears. Variational calculations were performed using a multiparameter Gaussian functions with correlation multipliers. The ground state energy of bipolaron is E 2 =-0.542169 E h * for η = ε ∞ /ε 0 = 0, where ε ∞ and ε 0 are the high-frequency and static dielectric constants of the crystal, respectively, E h * is the effective Hartree energy. The binding energy of bipolaron was calculated with respect to the double energy of 2D polaron obtained for wave function, consisting of 5 Gaussian exponents. The ground state energy of 2D polaron is E 1 =-0.202366 E h * for η = 0. The critical value of the ionicity parameter η corresponds to η с ≈ 0.2. At η > η c , 2D bipolaron breaks up into two 2D polarons.

Short-range order (SRO) in the liquid AlÀ NiÀ Sn alloys has been investigated using the X-ray diffraction method and Reverse Monte Carlo simulations. Obtained results point out a microinhomogeneous structure of AlÀ SnÀ Ni melts with Sn content between 10 and 65 at.% due to the presence of atomic clusters with the structure of liquid Sn and atomic clusters with NiÀ Sn coordination. The influence of the atomic size ratio (size factor) and pair atomic interactions (energy factor) on the short-range order of the investigated ternary melts are discussed. There is a competition between Al and Sn atoms in the formation of the SRO around Ni atoms due to the difference in bond energy in NiÀ Al and NiÀ Sn pairs. This competition, as well as a bigger radius of Sn atoms, results in the formation of atomic clusters with liquid Sn-like local atomic structure.

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