upward

Defects

Kolobov A V, Kondo M, Oyanagi H, Durny R, Matsuda A, Tanaka K, Experimental evidence for negative correlation energy and valence alternation in amorphous selenium, PRB 56, R485 (1997)

Vanderbilt D, Joannopoulos J D, Theory of defect states in glassy selenium, PRB 22, 2927 (1980)