Theoretical investigation of phase equilibria by the continuous displacement cluster variation method

By employing the continuous displacement cluster variation method, order - disorder transition behavior of a twodimensional square lattice is investigated. It is demonstrated that the distribution of displaced atoms around a Bravais lattice point continuously changes with temperature. The additional freedom of atomic displacement contributes to the entropy and thermal lattice expansion is confirmed. Finally, it is shown that the order - disorder transition temperature decreases as compared with the one by the conventional cluster variation method in which no local atomic displacements are allowed.