Hi This semester my group and I are calculating the band structure of silicone (bulk and nano crystals). In bulk silicon a indirect band gap occurs, where the highest occupied valence band and the lowest unoccupied conduction band are situated at different k-values. Does anyone know why this actually happens? If you have some literature that gives a valid explanation I would appreciate it. Another interesting thing is when quantum confining silicon structure the indirect band gap becomes direct. Does anyone know why reducing the size of silicon result in a more direct band gap? Also here if anyone has some literature that explains it I would appreciate it. Thanks!