Ab initio and Raman study of medium range ordering in GeSe2 glass

• Detailed ab initio density functional theory and Raman studies of medium range ordering in GeSe2 glass.
• Medium range order structures in GeSe2 glass consisting of even member rings of different sizes.
• Big 16-member rings topologically similar to high temperature β-GeSe2 realized in GeSe2 glass.
• Homopolar GeGe and SeSe bonds in g-GeSe2 are realized through five member rings.
• Odd and even member ring model of medium range order in g-GeSe2 is proposed.

High resolution Raman spectra of GeSe2 glass were measured and fitted using individual Gaussian components. The structural origin of the components were interpreted using the results of ab initio density functional theory calculations performed on GenSem nanoclusters (n = 2–6, 12; m = 6–9, 12, 14–16, 30) which represent the local structure of GeSe2 glass and on some “defect” GenSem clusters that are thought to be related to the inhomogeneity of the structure at the nanoscale. The calculated vibrational properties of GenSem nanoclusters and their couplings with the short- and medium-range order structure formations in GeSe2 glass are analyzed and discussed.