First principles calculations of electronic properties and mechanical properties of bcc molybdenum and niobium

The first principles calculations based on the density functional theory are performed to study the elastic properties and mechanical properties on Mo and Nb. It is found that the C ₁₁, C ₁₂ and C ₄₄ of metal Mo and the C ₁₁ and C ₁₂ of Nb are consistent with that of the experimental value and other calculated results. However, C ₄₄ of Nb is underestimated. In order to probe the reason why the C ₄₄ would be underestimated by theoretical calculation, we calculated the density of sated and Fermi surface of metal Nb and Mo. It is found that the most probable reason of underestimate C ₄₄ is related to the nesting properties of the Fermi surface which produce a Van Hove singularity in the electronic density of the state closed to the Fermi level. The ideal tensile strengths along [111] direction of bcc Mo and Nb is calculated. It is found that both materials exhibit dissimilar mechanical behaviors: The stress of Nb exists a turning point at the strain 8%, which is different from the behavior of Mo.