Phenylacetylene dimer: Ab initio and DFT study

Graphical abstract: The most stable conformer (antiparallel) of the phenyacetylene dimer. Highlights: ► We checked out various DFT approaches in the phenylacetylene dimer examination. ► The B97D, ωB97X-D, and M06-2X structures have the largest binding energies. ► The B3LYP is not an appropriate tool to investigate the phenylacetylene dimer. - Abstract: Phenylacetylene (PHA) consists of two substantially different subunits: the phenyl ring (aromatic) and the acetylenic (aliphatic) moiety. Both groups are represented by relatively high electron density caused by highly delocalized π-electron clouds. Here, we performed a detailed analysis of the phenylacetylene dimer which is characterized by a variety of non-covalent interactions like π–π stacking and H–π hydrogen bonds. We carried out geometry optimization of the phenylacetylene dimer at the counterpoise corrected MP2, MP2, B97D, ωB97X-D, M06-2X, and B3LYP levels of theory. For all the optimized structures, we calculated harmonic vibrational frequencies to assure that all the conformers are local/global minimum energy structures. Different levels of calculation predict different structures. Thus, for important structures, we computed binding energies at the complete basis set limit (CBS) of CCSD(T) theory. We conclude the antiparallel structure is the most stable. The formation of the phenylacetylene dimer is mainly driven by dispersion forces, however, the electrostatic interactions are also significant, which is confirmed by SAPT-DFT calculations. Hobza et al. reported counterpoise corrected MP2 results; however, we focus on DFT results