GaAs (111) and (1’-.2m’’.3m’¯ ’.2m’’-.3m’ 1’-.2m’’.3m’¯ ’.2m’’-.3m’ 1’-.2m’’.3m’¯ ’.2m’’-.3m’ ) surfaces and the GaAs/AlAs (111) heterojunction studied using a local energy density

We use a local energy density scrE(r) within density-functional theory to study GaAs (111) and (1{} 1{} 1{}) surfaces, and the GaAs/AlAs (111) heterojunction. We use scrE(r) to calculate the formation enthalpy of a single isolated GaAs (111) and (1{} 1{} 1{}) surface, which is not possible with the use of conventional total-energy methods. We are able to address questions related to the stability of these surfaces. Our methods also apply to heterojunctions where we consider GaAs/AlAs (111) as a prototype. We use scrE(r) to calculate the formation enthalpy of the Ga-rich and Al-rich interfaces, which are distinct and which are both inherent in the supercell geometry.