[en] Theoretical or Mathematical/ ab initio calculations ; antimony compounds ; bond lengths ; electronic structure ; germanium compounds ; molecular dynamics method ; noncrystalline structure ; optical conductivity ; phase change materials/ phase change materials ; metastable crystalline phase ; amorphous phase ; amorphous structure ; electronic properties ; ab initio molecular dynamics ; bond length ; Peierls-distortion ; electronic gap ; optical conductivity curve ; GeSbTe/ A6140 Structure of amorphous, disordered and polymeric materials A7125T Electronic structure of crystalline semiconductor compounds and insulators A6185 Modelling and computer simulation of solid structure A7115A Ab initio calculations (condensed matter electronic structure) A7820D Optical constants and parameters (condensed matter)/ GeSbTe/ss Ge/ss Sb/ss Te/ss
[en] Ge1Sb2Te4 is one of the most commonly used phase change materials, due to the large optical and electrical contrast between a metastable crystalline phase and the amorphous phase. We use ab initio molecular dynamics to generate an amorphous Ge1Sb2Te4 structure. By analysing the distance distributions, we show that the structure can be analysed in terms of 21% of tetrahedrally coordinated Ge atoms and 79% of 3-fold Ge atoms. These are involved in distorted octahedral shells with bond length correlations that are similar to the a-GeTe structure as a consequence of a Peierls-distortion. The electronic properties are shown to be in reasonable agreement with the experiment with an electronic gap of 0.45 eV with. The optical conductivity curve is also in agreement with the experiment, with a maximal conductivity at an energy of ~3 eV. [All rights reserved Elsevier].