| Abstract
| - The equilibrium structures, vibrational properties, and interaction energies for four bimolecular complexes ofHCN and HNC (HCN···HCN, HNC···HNC, HCN···HNC, and HNC···HCN) were studied with ab initiomethods. Different electron correlation levels and basis sets up to CCSD(T)/6-311++G(2d,2p) were used inthe geometry optimizations and interaction energy calculations, and the vibrational frequencies were calculatedat the MP2 and MP3 levels of theory. To study the nature of the intermolecular interactions, an energydecomposition analysis was carried out. For the HNC···HCN complex, which possesses a hydrogen bridgebetween two carbons, the counterpoise-corrected interaction energy and its decomposition has been calculatedas a function of the intermolecular distance. The effect of subunit deformation on the interaction energy hasalso been considered. The results indicate that the HNC dimer has considerably stronger intermolecularinteraction than the HCN dimer, and the HNC···HCN complex is bonded as strongly as the HCN dimer. Thecomparison of the various properties of the complexes and the energy decomposition analysis in particularindicate that carbon can act as both a hydrogen acceptor and donor, and the resulting hydrogen bonds inthese complexes are relatively strong.
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