With the rapid progress in growth technologies such as molecular beam epitaxy (MBE), semiconductor heterostructures offer a convenient way for precise control of band gap. When a thin layer of, say, GaAs is sandwiched between layers of Ga1-xAlxAs, therr larger gap material (the alloy) acts as a simple potential barrier for electrons at the bottom of the conduction band of GaAs (Capasso and Magaritondo, 1988).

Heterojunctions of technological interests frequently have interfaces more complicated than the ideal model assumes. Thus, the band offsets in GASb/InAs may be different from InAs/GaSb because of the difference in growth order (M. W. Wang et al.., 1995). It is also found that band offsets are very sensitive to the strain (C. Ohler et al., 1995).

Experiments usually use XPS to determine band offsets with reference to core levels that are not sensitive to the interface. Similar strategy can be used in all-electron ab initio calculations . For pseudo potential calculations, the potential level bias across the interface must be determinded and added to the nominal band offsets between two sublattices (Alfonso Baldereschi et. al., 1988).The Gaussian Dual Space Density Functional Theory we developed here at Caltech can be used both in pseudo potential approximation as well as in all-electron. Such method is currently being generalized for ab initio molecular dynamics (Car-Parinello type).