Molecular interaction energies and optimal configuration of a cubane dimer

Abstract

ABSTRACT:We have studied the dependence of the binding energy of a cubane dimer on the mutual orientation of and the distance between the composing monomers employing the second-order Møller-Plesset perturbation scheme (MP2) with the ccpVDZ molecular basis set. We have found that the MP2 contribution from the molecular correlations is responsible for the bound state of the cubane dimer, whereas the Hartree-Fock contribution remains anti-bonding at all intermolecular distances. Starting with two molecules in the standard orientation and centers of mass at (0,0,0) and (0,0,d), respectively, the maximal binding energy is found at d ϭ 5.125 Å and one of the monomers rotated by 45°about the z-axis. This configuration implies that the hydrogen atoms belonging to different monomers tend to repel each other. The results are in agreement with experimental data on the optimal packing of cubane molecules in the solid state.

Orientational ordering in solid C60 fullerene-cubane

“…This procedure yielded the values bb = 2.07 Å, bb = 19.33K ϫ k B , and = 0.4. 5 Recently, ab initio energy calculations for several configurations of the cubane dimer have been performed by Nikolaev et al 43 Two categories of energy calculations are presented, for varying intermolecular distance and varying molecular orientations. Fitting the cubic cluster LJ model to all the data sets in Ref.…”

“…Fitting the cubic cluster LJ model to all the data sets in Ref. 43 simultaneously is impossible-a shortcoming of a general nature since any simple pair potential model never captures all the details of an intermolecular interaction. We do not need a highly accurate cubane-cubane potential since the…”

“…Indeed, the typical distance between two nearest-neighbor C 8 H 8 molecules in fullerene-cubane is about 10 Å, well beyond the optimal 6.5 Å intermolecular distance. 43 We therefore considered the parameters bb , bb , and as tunable, for our purposes, rather than to be taken from a fit to cubane-cubane interactions. A priori requirements for our potential constants are reproducing ͑i͒ a fcc phase with a lattice constant close to the experimental value a = 14.74 Å at room temperature, ͑ii͒ a structural phase transition at about T Ϸ 140 K, and ͑iii͒ a transition from freely rotating to frozen fullerene molecules at about the same temperature as the structural phase transition.…”