POTENTIAL FUNCTIONS FOR DESCRIBING INTERMOLECULAR INTERACTIONS IN CYANOACETYLENE CLUSTERS

Potential functions for describing interactions between cyanoacetylene molecules based on ab initio determined molecular properties and IMPT calculations are proposed. Electrostatic interactions are described b y a multipole expansion on atoms and midbond points; dispersion is exp ressed by a London-type function of atomic polarizabilities and induct ion is considered via a series of polarizabilities distributed over th e atoms. The repulsion contribution was determined by using a test-par ticle model involving a helium atom as probe particle. Two functions b ased on two basis sets of different size, viz. 6-311G* and 5S4P2D/3S2 P, were used. Cyanoacetylene dimer exhibits two minima corresponding t o a linear and an antiparallel configuration, respectively. The propos ed functions accurately reproduce the characteristics of the dimer min ima as derived from ab initio calculations at the Moller-Plesset (MP2) level. In addition, they can describe cooperativeness in larger clust ers; specifically, the dipole moment and interaction energy per molecu le increase with increasing number of constituent units in the cluster . The behavior observed is similar to previously reported findings for HCN clusters. (C) 1998 American Institute of Physics. [S0021-9606(98) 31143-5].