Atomic-scale structure of the glassy Ge2Sb2Te5 phase change material: A quantitative assessment via first-principles molecular dynamics

The amorphous structure of the phase change material Ge2Sb2Te5 (GST) has been the object of controversial structural models. By employing first-principles molecular dynamics within density functional theory, we are able to obtain quantitative agreement with experimental structural findings for the topology of glassy GST. To this end, we take full advantage of a thoughtful, well established choice of the exchange-correlation (XC) functional (Becke-Lee-Yang-Parr, BLYP), combined with appropriate options for the nonlocal part in the pseudopotential construction for Ge. Results obtained by using the Perdew-Burke-Ernzerhof (PBE) XC functional and a similar strategy for the Ge pseudopotential constructions are also presented, since they are very valuable and worthy of consideration. The atomic structure of glassy GST is characterized by Ge atoms lying in a predominant tetrahedral network, albeit a non-negligible fraction of Ge atoms are also found in defective octahedra.