The effect of vibrational degrees of freedom on the phase transition in a 2D Ising model

The aim of this work is to show how important small atomic vibrations can be for the equilibrium state of a binary alloy or a lattice gas of adatoms on a surface. Using the Monte-Carlo procedure and performing direct lattice dynamics calculations, the total (configurational plus vibrational) free energy of the system is obtained. The calculations show that, if the difference in the bond stiffness between like and unlike atoms is large, it is possible to introduce a renormalised interaction constant and to treat the system as Ising-like. For this case, the effects of lattice dynamics parameters on the order–disorder transition temperature are discussed.