Theoretical study of hydrogen bonds between acetylene and selected proton donor systems

The equilibrium structures, the binding energies, and the second‐order energy components of a series of hydrogen‐bonded complexes involving acetylene are studied. The strength of the binding energy of the selected systems (HF … HCCH, HCl … HCCH, HCN … HCCH, and HCCH … HCCH) was different, ranging from a very weak interaction to a strong interaction. Calculations have been carried out at both the Hartree–Fock and correlated (second‐order Møller–Plesset perturbation theory) levels of theory, using several different basis sets [6‐31G(d,p), 6‐311G(d,p), 6‐31G++(d,p), 6‐311G++(d,p), 6‐31++G(2d,2p) and 6‐311++G(2d,2p)]. The widely used a posteriori Boys–Bernardi counterpoise (CP) correction scheme has been compared with the a priori CHA/CE, CHA–MP2, and CHA–PT2 methods, using the chemical Hamiltonian approach (CHA). The results show that at both levels the CP and the appropriate CHA results are very close to each other. Only the monomer‐based CHA‐PT2 theory gives slightly overcorrected results, reflecting that the charge transfer and polarization effects are not taken into account in this method up to second order. We have also applied our earlier developed energy decomposition scheme in order to decompose the second‐order energy contribution into different physically meaningful components. The results show that at large and intermediate intermolecular distances, the second‐order intermolecular contribution is almost equal to the sum of different physically meaningful components (e.g., polarization, charge transfer, dispersion), while at shorter distances the slightly strong overlap effects fairly disturb this simple additivity. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005