Dynamical, dielectric, and elastic properties of GeTe investigated with first-principles density functional theory

The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We report the electronic energy bands, phonon-dispersion curves, electronic and low-frequency dielectric tensors, infrared reflectivity, Born effective charges, and elastic and piezoelectric tensors and compare them with the existing theoretical and experimental results, as well as with similar quantities available for other ferroelectric materials, when appropriate.

Figure 1

Calculated band structure of rhombohedral GeTe. The top of valence band is set to zero.

Figure 2

(a) Evolution of Born effective charge tensor components along the path of atomic displacement from the cubic $\lambda =0$ to the rhombohedral $\lambda =+1$ (or $-1$) phase. The distortion of the unit cell has been neglected. (b) The polarization difference evaluated using the Berry phase technique as a function of $\lambda$ at fixed cubic unit cell (circle) and fixed rhombohedral unit cell (star).

Figure 3

Calculated phonon-dispersion curves of ferroelectric GeTe at the theoretical lattice parameters.

Figure 4

Calculated IR reflectivity spectra of GeTe (without anharmonic damping).