Fermi surface nesting and pre-martensitic softening in V and Nb at high pressures

• First-principles total-energy calculations were performed for the trigonal shear elastic constant (C-44) of body-centred cubic (bcc) V and Nb. A mechanical instability in C44 is found for V at pressures of similar to 2 Mbar which also shows a softening in Nb at pressures of similar to 0.5 Mbar. We argue that the pressure-induced shear instability (softening) of V (Nb) is due to the intra-band nesting of the Fermi surface.

Nyckelord

tin orbitals theory

soft phonon mode

brillouin-zone

special points

energy method

approximation

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