Low Temperature Energy Phase Diagrams of Dimer Adsorption on Square Nanotubes With Attractive First Neighbor Interactions

We consider dimer adsorption on a nanotube with square lattice geometry that is an arbitrary number $M$ of atomic sites in normal cross-section. First-neighbor adsorbate-adsorbate interactions, $V$, are assumed to be attractive while second-neighbor interactions, $W$, are allowed to be repulsive, attractive or negligible. The effective potential energy per dimer, $\mu $, is the sum of the adsorbate-substrate interaction energy and the chemical potential of dimer molecules in the medium surrounding the nanotube. At low temperature, the energy phase diagrams are two-dimensional with parameters $u \quad = \quad W$/$V$ and $v \quad = \quad \mu $/$V$. These diagrams have been generated numerically for increasing values of $M$. They fall into two categories which depend on whether $M$ is even or odd. The occupational characteristics of the phases have analytic expressions in $M$. The occupational configurations of, and line boundaries between phases are determined.