  Chalcogenide alloys are materials of interest for optical recording and
non-volatile memories. We perform ab-initio molecular dynamics simulations
aiming at shading light onto the structure of amorphous Ge2Sb2Te5 (GST), the
prototypical material in this class. First principles simulations show that
amorphous GST obtained by quenching from the liquid phase displays two types of
short range order. One third of Ge atoms are in a tetrahedral environment while
the remaining Ge, Sb and Te atoms display a defective octahedral environment,
reminiscent of cubic crystalline GST.
