Ab initio studies on the van der Waals complexes of polycyclic aromatic hydrocarbons. II. Naphthalene dimer and naphthalene–anthracene complex

Abstract

Ab initio calculations were carried out for the naphthalene dimer and naphthalene–anthracene complex to determine their stable geometries and binding energies. Two medium-size basis sets of 6-31G*(0.25) and 6-31+G* were employed at the MP2 level. Five local minima were found for the naphthalene dimer, three of which were parallel-displaced type and the other two T-shaped type. The global minimum geometry was a parallel-displaced structure of a two-layer graphitic type (Ci point group), not the crossed form (D2d). Its energy calculated by the 6-31G*(0.25) and 6-31+G* basis sets was −7.62 and −6.36 kcal/mol, respectively. The naphthalene–anthracene complex showed four local minima, two of which were parallel-displaced type and the other two T-shaped type. The global minimum was a twisted parallel-displaced form (C2), in which the centers of both molecules lie on the same z-axis with their two long axes skewed at an angle of ≈40°. Its energy was −11.30 and −9.52 kcal/mol with the 6-31G*(0.25) and 6-31+G* basis sets, respectively. From these results a set of general rules for the stable geometry of the polycyclic aromatic hydrocarbon clusters were derived, which turned out to be the same as those previously deduced from other systems less directly relevant to polycyclic aromatic hydrocarbons: (1) a face-to-face configuration is unstable, (2) the T-shaped structure is stable, (3) the parallel-displaced structure is also stable. We also found some additional rules: (4) the energies of the T-shaped and parallel-displaced structures are quite comparable when the molecules are small, but (5) the parallel-displaced structure becomes more stable than the T-shaped one as the molecules become larger due to the nature of the π–π interaction. The interplanar distance of stable parallel-displaced structures was about 3.3–3.4 Å, while the plane-to-center distances of T-shaped structures was about 5.0–5.1 Å. We also discovered what we would call the integer rule for the binding energy of the polycyclic aromatic hydrocarbon clusters in that the binding energy varied linearly as the number of overlapping hexagons in the parallel-displaced structures. The ratio of binding energies for the benzene dimer, benzene–naphthalene complex, naphthalene dimer, and naphthalene–anthracene complex were nearly 1:2:3:4.

Far-IR and UV spectral signatures of controlled complexation and microhydration of the polycyclic aromatic hydrocarbon acenaphthene

“…in Ref. [30][31][32][33][34] that give insight into their preferred geometries. In a parallel spectroscopy study in the microwave range acenaphthenewater (Ace-W) 14 clusters were investigated, which revealed the first steps of PAH-water complex formation.…”

Investigation of the Benzene–Naphthalene and Naphthalene–Naphthalene Potential Energy Surfaces: DFT/CCSD(T) Correction Scheme

“…Such calculations are at the limit of current computational hardware for benzene dimer complexes and are certainly impractical even for the description of the dimer of the smallest PAH—the naphthalene dimer. It is therefore understandable that the naphthalene dimer complexes have mostly been investigated at the MP2 level of theory,8–11 which is, however, known to overestimate the interaction between weakly‐bonded aromatic hydrocarbon complexes (see for example, ref. 12, discussing the benzene dimer).…”

Comparison of Intrinsic Stacking Energies of Ten Unique Dinucleotide Steps in A-RNA and B-DNA Duplexes. Can We Determine Correct Order of Stability by Quantum-Chemical Calculations?

“…The d-polarization functions are capable of filling the gap between the interacting monomers, which significantly improves the description of base stacking interactions compared with the standard 6-31G* basis set. The MP2/6-31G*(0.25) method has been the most widely used ab initio technique to study aromatic stacking in the past literature 31,35,50,51,60,85,100,101,[107][108][109][110][111][112][113][114][115][116][117][118][119][120] and has only recently been replaced by CBS(T). The MP2/6-31G*(0.25) method is entirely sufficient to capture the nature of base stacking, and therefore all conclusions reported with this method remain qualitatively valid.…”