COMPARISON OF EXPERIMENTAL AND THEORETICAL ELECTRONIC CHARGE-DISTRIBUTIONS IN GAMMA-TIA1

Using critical voltage electron diffraction, Fox has recently determined the lowest seven X-ray structure factors of gamma-TiAl (L1(0) structure). We present here a comparison of these accurately measured (0.15%) structure factors with first-principles local density calculations, finding an agreement within 0.7% and an r.m.s. error of 0.013 e/atom. While such measurements are limited to the first few structure factors rho(G) (where G is the crystal momentum), theory is able to obtain rho(G) for arbitrarily high G. If we construct charge density deformation maps by Fourier summations up to the lowest measured G, the calculated and experimental density deformation maps agree very closely. However, if we include in the theoretical density deformation map high G values (outside the range accessible to experiment), qualitatively different bonding patterns appear, in particular between Ti atoms. Systematic study of the total, valence, and deformation charge densities as well as comparison with result for NiAl in the hypothetical L1(0) structure elucidate the bonding patterns in these transition metal aluminides.