Photo-induced volume changes in selenium. Tight-binding molecular dynamics study

Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se ₈ ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyze the photo-induced instability in amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photo-induced volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination.