Potential functions for describing intermolecular interactions in cyanoacetylene clusters

Abstract

Potential functions for describing interactions between cyanoacetylene molecules based on ab initio determined molecular properties and IMPT calculations are proposed. Electrostatic interactions are described by a multipole expansion on atoms and midbond points; dispersion is expressed by a London-type function of atomic polarizabilities and induction is considered via a series of polarizabilities distributed over the atoms. The repulsion contribution was determined by using a test-particle model involving a helium atom as probe particle. Two functions based on two basis sets of different size, viz. 6-311G** and 5S4P2D/3S2P, were used. Cyanoacetylene dimer exhibits two minima corresponding to a linear and an antiparallel configuration, respectively. The proposed functions accurately reproduce the characteristics of the dimer minima as derived from ab initio calculations at the Mo/ller–Plesset (MP2) level. In addition, they can describe cooperativeness in larger clusters; specifically, the dipole moment and interaction energy per molecule increase with increasing number of constituent units in the cluster. The behavior observed is similar to previously reported findings for HCN clusters.