# First principles calculation of the dipole moments of small mixed Ge/Te semiconductor clusters

Zeitschrift für Physik D **40**, 182 - 185 (1997)

# First principles calculation of the dipole moments of small mixed Ge/Te semiconductor clusters

We investigate the structural and electronic properties of the small mixed semiconductor clusters GeTe, Ge_{2}Te, GeTe_{2} and Ge_{2}Te_{2} by means of first principles supercell calculations using the local density approximation and the pseudopotential plane wave method. The cluster geometry is optimized using a conjugate gradient method. For GeTe_{2} we confirm the linear structure (D_{¥h}) suggested by recent experiments. For Ge_{2}Te we obtain an equilateral triangle as the equilibrium structure. For Ge_{2}Te_{2} we obtain a deformed tetrahedrom (butterfly C_{2v} symmetry). For each of these molecules we compute the dipole moment in the equilibrium geometry and in selected geometries near to equilibrium corresponding to states higher in energy by a few tens of meV. For the equilibrium state of Ge_{2}Te and Ge_{2}Te_{2} we obtain permanent dipole moments smaller than those estimated from recent experiments at room temperature. For selected low lying excited states of these clusters, which have elongated Ge-Te bond length, we obtain enhanced dipole moments, improving the agreement with the ones estimated from experiments.