The band structure of vanadium monocarbide is calculated by the tight-binding method. A set of ten Bloch sums of the 3d, 4s and 2s, 2p states of the free V and C atoms is used as the basis functions. The secular equation is solved at the 89 points of the 1/48th of the Rrillouin zone. The density of states and partial density of states histograms are obtained. The populations of the orbitals show that about 0.5 electrons transfer from the carbon to the vanadium orbitals. However. the distribution of the electron rharge density points out that there are strong directional metalnon-metal bonds, in which carbon cannot be considered as a positive ion. Ha nepexoir, HMepHo 0,5 a n e~~p o~a c op611~anefi ymepona K MeTanny. OnHaI

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A method of constructing the exchange potential in a crystal as a superposition of effective one-centre exchange potentials is considered. Avaraging is used over atomio wave functions located on different lattice sites. The results obtained are compared with atomic exchange potentials calculated by the Slater approximation and by averaging the exchange term in the atomic Hartree-Fock equation. B pa6oie PaCCMOTpeHa BOaMOWEOCTb IIOCTpOeFIEl R 06MeHHOrO n0TeHUHana B TeHUHaJIOB, IIyTeM YCpeWeFIkiX X I 0 ELTOMWM BOJIHOBbIM @YHKUHFIM, qeHTpHpOBaH-Kpm-ranne B mine cynepnoamm e@@emmmsx onHoueaTposMx O~M~H H M X no-H~I M Ha paannusmax yanax perueTm. IIonynemme peaynmam cpaBmsawrcH c aT0M-n O~M~H H~I M H noTemwanam, pacmTaHmMH B n p u 6 n~x e~i~~ Cna~epa, H nyTeM ycpejmemuz o 6~e~~o r o noTemuiana B ypamemu XapTpH-OoHa EJIX aToMa.

The results of calculations of the electron energy spectrum and the contribution of atomic states to the formation of band structure of vanadium, niobium, and zirconium monocarbides based on the tight-binding method arc reported. The calculations were performed in twoecntrc approximation, taking into account the ns and ( n -

Dedicated to Prof. Dr. Dr. h.c. P. GORLICH, on the occasion of his 65th birthday Basing on the general conceptions of the band structure of stoichiometric IVa subgroup transition metal monocarbides and assuming two types of atomic interactions a conduction band model for nonstoichiometric carbides has been elaborated which takes into account the vacancies in the carbon sublattice. It is assumed that the formation of vacancies is accompanied by the appearance of local electronic levels in the vicinity of the Fermi level of stoichiometric carbide which, in the case of high concentrations of C-vacancies, form a subband of unscreened Me-Me bonds. This results in a filling of the Me-C band, a shift of the Fermi level into the Me-Me band, followed by an increase of the electron density of states and an increase of the Ferrni level. The increasing density of states leads to an increase in the magnetic susceptibility