Effect of nonmonotonic changing of surface coverage in multisite adsorption models with possibility of different orientations of molecules with respect to solid surface

The reasons for nonmonotonous changing of surface coverage as function of chemical potential in the multisite adsorption models (with allowance for the possibility that molecules can be oriented in a different manner with respect to the solid surface) are revealed in this work. It is demonstrated that this behavior of the surface coverage as function of chemical potential is determined by either the sequence of ordered structures being formed or by the emergence of a stable interface between the ordered phases at temperatures above the tricritical point.