Noncovalent interaction of meso-tetraphenylporphine with C60 fullerene as studied by several DFT methods.

We performed density functional theory (DFT) calculations of noncovalently bonded 1:1 complex of meso-tetraphenylporphine H2TPP with fullerene C60. The functionals used were PW91, PBE and BLYP of general gradient approximation (GGA), as well as PWC and VWN of local density approximation (LDA) as implemented in the DMol3 module of Materials Studio package from Accelrys. The computed geometries were compared to the experimental X-ray diffraction data obtained elsewhere for rhombohedral and monoclinic H2TPP + C60 crystalline complexes. If the correlation coefficient between the calculated and experimental data is applied, the covalent bond lengths and angles within H2TPP unit are best reproduced by BLYP functional, whereas PWC and VWN are least precise. On the other hand, PWC and VWN are the best functionals in reproducing the separations between H2TPP and C60 found from X-ray diffraction analysis: the LDA-calculated N(H2TPP) ... C(C60) distances are of about 2.9-3.0 angstroms, whereas the corresponding experimental values are of ca. 3.0-3.1 angstroms. Next are PW91 and PBE functionals, giving N(H2TPP) ... C(C60) distances of ca. 3.5-3.6 angstroms. BLYP produced the separations of around 4.0-4.1 angstroms, which are inconsistent with both X-ray data and the results produced other functionals. We also analyzed functional-dependent variations in formation energies, electrostatic potential, HOMO, LUMO and charge transfer. We concluded that of DFT functionals incorporated into DMol3 module and tested in this study, PWC and VWN are the most adequate ones, and BLYP is the least recommended one for the studies of noncovalent interactions of porphyrins with carbon nanoclusters.