Ab initio calculations were carried out for dimers of acetylene and a polyyne chain with two to five triple bonds at the MP2 level. The structure and energies of several symmetry-constrained structures were found and used to guide refinement of a model potential that could be applied to longer polyyne chains. The slice of the intermolecular potential surface for sliding an acetylene along the polyyne chain in a T-shaped orientation was mapped and showed shallow corrugation over a large region. This amounts to slipperiness in this type of weak bonding.