First principles study on the structural properties and electronic structure of X2B (X = Cr, Mn, Fe, Co, Ni, Mo and W) compounds

First principles calculations are performed to study the stability, electronic and structural properties of X2B (X = Cr, Mn, Fe, Co, Ni, Mo and W). The calculated cohesive energy and formation enthalpy of these compounds both have negative values, which indicate that they are thermodynamically stable structures. The ground states of Cr2B and Mn2B are anti-ferro magnetic: Fe2B and Co2B are ferromagnetic; Ni2B, Mo2B and W2B are paramagnetic. The calculated local magnetic of Fe2B is 1.962 mu(B)/Fe, and for Co2B is 1.182 mu(B)/Co. They are comparable to the values of Fe3B (1.97 mu(B)/Fe) and Co3B (1.18 mu(B)/Co), but smaller than pure Fe and Co. The observed magnetic behaviors of X2B compounds can be explained by Stoner's model. Two main peaks are observed in the calculated PDOS (partial density of states) of these compounds (P1 and P2). P1 is caused by strong covalent X-B bonds and P2 is attributed to metallic X-X bonds. (C) 2008 Elsevier B.V. All rights reserved.