“…To our knowledge the problem of SLs with various growthaxis directions has often been addressed by means of the envelope function approach (Kajikawa, 2012;Los et al, 1995;Hayakawa, Suyama et al, 1998a,b;Hayakawa, Takahashi, Kondo et al, 1988a,b;Haya-kawa, Takahashi, Suyama et al, 1988;Vina & Wang, 1986;El Khalifi et al, 1990;Gil et al, 1990) and rarely by other methods such as the tight-binding approach (Wang & Ting, 1995) or the first-principles methods (Assa Aravindh et al, 2012;Rubio et al, 1994;Picozzi et al, 1997;Magri, 1990;Bungaro & Rabe, 2002;Tair et al, 2007;Badi et al, 2008). The first-principles methods are particularly needed to investigate microscopically these specific systems.…”