MMC model calculations were performed for the trimer, ðHCCHÞ2–HCN, and critical points were located. The most stable minimum energy structure was a cyclic species and this provided a starting structure for the minimum energy search
with ab initio calculations. To a good extent, all the optimum arrangements between pairs of molecules in the trimer structures showed either a near T-shaped or near linear arrangement that mimicked one or the other of the two dimer minima.