Ab initio calculations have been performed to determine the structures and interaction energetics of (HCCH)(2)-HCN and certain related clusters. The clusters have arrangements of each HCN-HCCH pair being essentially either T-shaped, with the HCN as a proton donor, or linear, with the acetylene as the proton donor to the nitrogen end of HCN. Three-body energetic features are small as are the polarization energy effects. A model potential has been applied to these and larger clusters. Though strongly polar, substitution of one HCN for acetylene in a pure cluster yields small structural differences. (C) 2003 Published by Elsevier Science B.V.