A system containing silicon vacancies on the surface of SiC-3C silicon carbide has been studied by the density functional theory. It is shown that the initial state of a system with a zero magnetic moment is metastable. The Si atom on the vacancy thread is a strong centre of attraction for electrons, despite their Coulomb repulsion. Therefore, it is advantageous for an electron from a weakened carbon atom in the C-C bond to tunnel to a silicon atom in the Si-C bond and thereby reduce its length from 1.96 Angstrem to 1.92 Angstrem. Relaxation of the elastic energy of the Si-C bond provides a decrease in the total energy by 0.29 eV. During tunnelling, the electron reverses its spin, doubling the total magnetic moment. Thus, the negative Hubbard correlation energy of electrons (negative-U) is realized in the system. In the presence of an external magnetic field, electrons can tunnel through any closed loop of vacancy threads, ensuring the diamagnetism of this material. Keywords: silicon carbide, silicon vacancies, negative correlation energy, magnetic moment, negative-U, diamagnetism.

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