Structure models of the GST phases. (a) Metastable crystalline GST (m-GST). (b) Intermediate m-GST (shift) structure, in which the Ge atoms occupy the fourfold tetrahedron sites with lowest energy. (c) Amorphous GST obtained at zero temperature using modified m-GST structures (am-GST), in which the tetrahedron sites were initially occupied. (d) Amorphous GST obtained by high temperature MD DFT calculations (a-GST). The Ge, Sb, and Te atoms are indicated in green (light gray), blue (medium gray), and red (dark gray), respectively.
Pair correlation functions of various GST phases. (a) Amorphous GST obtained by MD calculations (a-GST) using hexagonal (black lines) and cubic (green) supercells. (b) Amorphous GST obtained by MD calculations (a-GST, black lines). Amorphous GST obtained from occupation of tetrahedron sites in m-GST and complete relaxation (am-GST, red lines). Metastable GST phase (m-GST, blue lines, scaled by 0.50).
Potential energy path for atomic displacements of Ge atoms along of the RS  direction of GeTe. (a) Distorted RS structure. (b) Perfect RS structure. (c) Long Ge–Te bond ZB structure. (d) Graphitelike structure. (e) Perfect ZB structure. (f) RS-layer structure.
Bond lengths (in angstroms) of GST in the amorphous and crystalline phases.
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