P. Nikitas, APPROPRIATE AND INAPPROPRIATE STATISTICAL-MECHANICAL TREATMENTS FOR PHASE-TRANSITIONS AT ELECTRIFIED INTERFACES, Journal of electroanalytical chemistry [1992], 408(1-2), 1996, pp. 1-4
The prerequisites for a statistical mechanical treatment of phase tran
sitions of adsorbed layers on electrode surfaces to give results compa
tible with both classical thermodynamics and experiment are studied. I
t is shown that the use of the charge density as the independent elect
rical variable, either in the canonical ensemble or the grand ensemble
partition function of simple models, leads to artifacts which are at
variance with thermodynamics. In contrast, the generalised ensemble De
lta, presented in Nikitas et al. (J. Electroanal. Chem., 317 (1991) 43
), which uses the potential drop across the layer which undergoes the
transition as independent variable, gives results compatible with both
experiment and thermodynamics under all circumstances. The results ob
tained are compared with the predictions of Guidelli and Aloisi's thre
e-dimensional lattice model of TIP4P water molecules. It is shown that
in this case the choice of the charge density as independent variable
leads to an incomplete description of the two-dimensional phase trans
ition properties, since the vertical steps obtained in the adsorption
isotherms at constant charge density may either indicate a new type of
phase transition which has not been observed experimentally yet or th
ey are artifacts which do not represent the properties of the phase tr
ansition.