Transition metals and their carbides and nitrides: Trends in electronic and structural properties

A study of the structural and electronic properties of selected transition metals and their carbides and nitrides is presented. We focus on assessing trends of possible importance for understanding their hardness. Lattice con stants, bulk moduli (B-o), and charge densities are calculated using the lo cal density approximation with a pseudopotential plane wave approach. An fe e lattice is employed for the transition metal elements in order to make co mparisons and study trends relateable to their carbides and nitrides. Our r esults show that both increasing the number of valence d electrons and the presence off electrons in the core lead to larger (B-o). Charge density plo ts and histograms enable us to explain the nature of the charge distributio n in the interstitial region for the different compounds considered. In add ition, we include the heavier elements seaborgium, bohrium, and hasnium in order to test further trends. Surprisingly, the calculated B-o for Hs is co mparable to that of diamond. [S0163-1829(99)03630-9].