97-21U

The XXZ--model was investigated within two--particle cluster approximation with two variational parameters $\varphi^z$, $\varphi^x$. The long--range interaction $J$ was taken into account in the framework of mean--field approximation. At various values of the anisotropy parameter ${\alpha}/{\gamma}$ ($K^{zz}=\gamma K$, $K^{xx}=K^{yy}=\alpha K$, $J^{zz}=\gamma J$, $J^{xx}=J^{yy}=\alpha J$, $K$ -- short--range interaction) and long--range interaction $J$, phase diagrams were constructed and temperature dependences of $\langle S^z \rangle$, $\langle S^x \rangle$, entropy, specific heat, and static susceptibility were calculated. It was shown that at ${\alpha}/{\gamma} \geq 1$ two--particle cluster approximation gave qualitatively incorrect results in a low--temperature region.