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 b e for the equilibrium state of a binary alloy or a lattice gas of adatoms o n a surface. Using the Monte-Carlo procedure and performing direct lattice dynamics calculations, the total (configurational plus vibrational) free en ergy of the system is obtained. The calculations show that, if the differen ce in the bond stiffness between like and unlike atoms is large, it is poss ible to introduce a renormalised interaction constant and to treat the syst em as Ising-like. For this case, the effects of lattice dynamics parameters on the order-disorder transition temperature are discussed. (C) 1999 Elsev ier Science B.V. All rights reserved.