New sight into the structure of selenium: Four-valence Se in glass

A comparison of the known structural data, with our quantum-chemical results for a-Se, leads to the conclusion that a neutral four-valence state, Se40, represents the lowest-energy (0.4 eV) defect, whose concentration is about 10% in the glass and greater in the melt. These results are expanded to other substances with the conclusion that the ability of a chemical bond system to generate low-energy network-linking alternative bonds (or 'defects') is a key property that distinguishes a group of glass-forming substances.