Bond-changing structural rearrangement in glassy As3Se7 associated with long-term physical aging

Ab initio quantum chemical calculations with RHF/6-311G⁎ basis set are performed to justify destruction-polymerization transformations in glassy g-As3Se7 possible during long-term natural physical aging. It is shown that switching of two AsSeSeAs bridges into short AsSeAs and long AsSeSeSeAs fragments is energetically favorable, testifying thermodynamic possibility for such structural changes. This finding is in good agreement with previous experimental observations for g-As3Se7 performed with Raman scattering, NMR and high-resolution XPS measurements. Simulation data suggest that physical aging in Se-rich As–Se glasses can be treated as a unique cooperative relaxation process accompanied by atomic rearrangement within homopolar SeSe bonds incorporated between two neighboring AsSe3/2 pyramids.