Series Expansion for the Monomermdash;Trimer Problem. I. General Formulation and Application to the Square Lattice

摘要

The combinatorial method of Nagle for monomermdash;dimer mixtures is extended to the monomermdash;trimer case. It turns out that the method becomes much more sophisticated: the relevant graphs involve two different types of edges and their weights are complicated functions of the natural expansion variablexof the problem (related to the trimer concentration). The method is applied to assemblies of (a) rectilinear, (b) bent, and (c) flexible trimers on the square lattice. The residual entropy of rectilinear trimers at close packing is estimated,SRsol;kequals;0.45.