The mechanism of the displacive phase transition in vanadium dioxide

The mechanism of the displacive phase transition in VO2 is unravelled through mapping of the free energy over the space spanned by two soft phonon modes. These modes crucially describe two independent Peierls distortions along chains of edge-sharing VO6 octahedra, which transform the tetragonal into the monoclinic phases on cooling. Calculation of potential energy employs our successful model of interatomic potentials, as current ab-initio calculations are intractable. The free energy is calculated within the quasi-harmonic approximation with thorough sampling of the Brillouin zone. Main experimentally observed features of this first order transition are reproduced, including the critical temperature.