In the recent years, Ab Initio Density Functional Theory calculations have proven to be extremely useful in the production of structural models helping to interpret the output of many experiments, such as diffraction, x-ray absorption as well as other kind of spectroscopies. In this work, we present the results of a series of simulations of GeTe- Sb2Te3 pseudobinary amorphous systems and address the relation between the electronic properties (localization,conductivity) of the amorphous phase and those of the relevant crystal phase. We use a new implementation of XANES spectra calculations within DFT and PAW potentials to perform a fully ab initio calculation of these spectra, including the self-consistent treatment of the core-hole effects. This approach allows to relate the phase change contrast to a moderate modification of the local environment of the Ge atoms and to the Peierls distortion and emphasizes the role of fluctuations and disorder.
We also study the effect of carbon and nitrogen incorporation inside the GeTe material. Strong carbon doping has been shown to increase significantly the recrystallization temperature of GeTe. Using DFT simulated annealing, we obtain a structural model that reproduces the trends observed by X-ray diffraction, showing the strong structuration of the amorphous phase through CGe4 units and long carbon chains.