Phonon instability and charge density wave in U2Ti

Phonon dispersion, structural distortion and the elastic properties of U2Ti are studied using ab-initio techniques. Our calculations revealed an instability in the hexagonal structure of U2Ti which is not observed in the earlier studies on this system. This instability is demonstrated through the imaginary phonon frequencies found around the A-point in the Brillouin zone. This instability leads to a Peierl's type of dimerization of U atoms along Z direction which will result in the formation of charge density wave (CDW) in the system. The dimerization leads to a new ground state structure in the system whose unit cell evolve by the doubling of the original cell along the Z direction. Our calculations further showed that the CDW exist in the system up to a pressure of 4 GPa.