Stochastic Search of Molecular Cluster Interaction Energy Surfaces with Coupled Cluster Quality Prediction. The Phenylacetylene Dimer

We report a stochastic search methodology on the basis of dispersion-augmented density functional theory (DFT), aimed at finding low energy isomers of the phenylacetylene dimer as well as methane and benzene dimers. Stochastic search of the molecular cluster interaction energy surfaces was carried out with the computationally inexpensive dispersion-augmented, third-order self-consistent charge density functional tight-binding (DFTB3-D) method, and energetically low-lying molecular cluster geometries were identified, including several that had previously been optimized at the MP2/cc-pVTZ level of theory and had single point interaction energies evaluated at the coupled-cluster singles, doubles, and perturbative triples (CCSD­(T)) level of theory in the complete basis set limit (Maity, S. et al. <i>Phys. Chem. Chem. Phys</i> <b>2011</b>, <i>13</i>, 16706). In addition, the search procedure identifies several additional low-energy isomers that map a reaction path, rotating one monomer through a full 360° relative to the first. We found that binding energies from long-range corrected functional combined with the local response dispersion correction (LC-BOP+LRD) yields binding energies that are within 1 kJ mol^–1 of the CCSD­(T)/CBS results for both π-stacked and CH···π structures. In contrast, other functionals and second-order Møller–Plesset perturbation methods favored one binding motif or the other and therefore are not ideal to describe a global potential energy surface