ИСТИНА

Novel carbon nanomaterials such as graphene and endofullerenes continue to attract much attention of researchers from various scientific fields. This is related to fundamental aspects of their characteristics, and also, is certainly driven by numerous possible applications in physics, chemistry, material science and biology. One of the discussed application is to use boron-containing endofullerenes for the boron neutron capture therapy (BNCT) in oncology treatment. Aiming at that goal, in the presentation, I will discuss various conformations in the exohedral and endohedral molecular complexes of boron and beryllium with the C60 fullerene, studied on the basis of ab initio molecular calculations. In particular, we have studied theoretically the bound states of one and two boron atoms in the exohedral and endohedral C60 fullerene. The optimal position of one boron atom is found above the midpoint of the C60 double bond in the exohedral complex, and at the center of C60 or below a carbon atom in the endohedral complex. However, the optimal position of a boron atom is often altered when the second boron atom is added to the molecular complex. Remarkably, some of these optimal arrangements have different spin states: in the exohedral complex B2C60 S = 1, in the endohedral B2@C60 S = 2 (as in the isolated B2 molecule) The effective (Bader) charge of boron in these configurations varies appreciably – from 0.06e at the center of C60 to 2e in the B2C58 molecule with two boron atoms substituting for two carbon atoms in C60. We have also studied the potential barriers for the penetration of atomic beryllium or boron inside the C60 fullerene by performing ab initio density functional theory (DFT) calculations (including the dispersion interaction) with three different variants for the exchange and correlation: B3LYP (hybrid functional), PW91 and PBE. Four principal trajectories to the inner part of C60 for the penetrating atom (i.e. Be or B) have been considered: through the center of six-member-carbon ring (hexagon), five-member-carbon ring (pentagon), and also through the center of the double C-C bond (D-bond) and the center of the single C-C bond (S-bond). Averaging over the three DFT variants yields the following barriers for beryllium penetrating inside a deformable fullerene: 3.2 eV (hexagon), 4.8 eV (S-bond), 5.3 eV (D-bond), 5.9 eV (pentagon). These barriers correspond to the slow and adiabatic penetration of Be, in contrast to the fast (non-adiabatic) penetration through the rigid cage of C60 resulting in 5.6 eV (hexagon), 16.3 eV (pentagon), 81.8 eV (S-bond) and 93.4 eV (D-bond). The potential barriers for the boron penetrating inside deformable/rigid C60 are: 3.7/105.4 eV (D-bond), 4.0/86.8 eV (S-bond), 4.7/7.8 eV (hexagon), 6.8/14.0 eV (pentagon). The binding energy of both Be@C60 and B@C60 is negative (Ec < 0), which implies that the potential barriers for Be and B escaping from the inner part of C60 are higher by the value of –Ec  0.84 eV for Be and 0.81 eV for B. The considerable reduction of the potential barriers for the deformable fullerene is ascribed to the formation of the corresponding Be-C and B-C bonds. We discuss the difference between the lowest barriers for Be and B, compare three variants of DFT, and analyze the role of the dispersion interaction.