  On the basis of the first principles simulation, the structure, formation
enthalpy, and mechanical properties (elastic constant, bulk, and shear modulus
and hardness) of five Nb-doped Ni systems are systematically studied. The
calculated equilibrium volume increases with the Nb concentration increasing.
The computational elastic constants and formation enthalpy indicate that all
Nb-doped Ni systems are mechanically and thermodynamically stable in our
research. The hardness of these systems also be predicted after the bulk
modulus and shear modulus have been accurately calculated. The results show
that the hardness increases with the Nb concentration increasing when the Nb
concentration below 4.9%, beyond which the hardness will decrease within the
scope of our study.
