We report the structural, elastic, mechanical and electronic properties of nitrogen (N)-doped cubic diamond up to 25%N doping concentrations in the steps of 5%N dopant. Our calculations were performed with the generalizedgradient approximation functional of density functional theory with the Perdew–Burke–Ernzerhof exchange–correlation energy through virtual crystal approximation. Cubic diamond shows a structural stability up to 15%N doping and it becomes instable above this dopant concentration. The changes for the typical cubic elastic constants, bulk, shear and Young’s moduli, Poisson ratio, anisotropy, Pugh ratio, Kleinman parameter and electronic band structures of cubic diamond vs. applied doping percentages were also evaluated. The obtained results for these parameters were found to bestrictly dependent on the dopant concentration. Although cubic diamond is a well-known insulator, it displays a metallic character even under the doping of 5%N and keeps this trend for higher doping concentrations.

We theoretically investigated the structural, elastic and mechanical properties of Ti–15Nb–$x$Ge alloys with $x = 0.8$, 1, 1.2, 1.4, 1.6 and 1.8 (wt%) compositions for the first time. Theoretical calculations were performed with thegeneralized gradient approximation (GGA) functional within density functional theory (DFT). We employed the Perdew–Burke–Ernzerhof (PBE) scheme and the virtual crystal approximation (VCA) in this study. We determined the elasticconstants, bulk, shear and Young’s moduli, Pugh ratio, Poisson’s ratio, universal anisotropy and hardness of all the alloys under varying Ge% concentrations. All studied compositions of the alloys show structural stability. Young’s modulivalues were obtained as 43 and 14.8 GPa for Ti–15Nb–0.8Ge and Ti–15Nb–1.8Ge alloys, respectively, which compare well to the Young’s moduli range of human cortical bone with 10–30 GPa. Except the Poisson’s and Pugh ratios, all other computed parameters of the alloys were found to decrease under increasing Ge concentrations. Further, all investigated alloys exhibit desired ductile mechanical behaviour of biomaterials and calculated hardness values of these alloys are satisfactory with the hardness of human teeth dentin.