Core-Shell Heterostructures for Photovoltaic Energy Conversion Igor Vasiliev, Department of Physics, New Mexico State University, Las Cruces, NM 88003 Our research focuses on theoretical prediction of the structural, electronic, and optical properties of core-shell semiconductor nanoparticles. The goal of this project is to expand the knowledge of chemistry and physics of semiconductor heterostructures and accelerate the development of composite materials for efficient conversion of solar energy. Structural optimization of core-shell semiconductor nanoparticles: Two types of core-shell nanoparticles were considered in our study: traditional, in which a core of a narrow gap semi-conductor is covered with a shell of a wide gap material, and inverted, in which a wide-gap core is enclosed in a narrow-gap shell. The structures of nanoparticles were optimized using ab initio computational methods based on density functional theory. The surfaces of nanoparticles were passi-vated with partially charged hydro-gen atoms. This approach removed the electronic states associated with the surface atoms from the gap. We found that CdSe/ZnSe and ZnSe/CdSe nanoparticles based on the sphalerite form of CdSe were lower in energy than those based on the wurtzite form of CdSe. Inverted (a) and traditional (b) core-shell semiconductor nanoparticles Optimized structures of ZnSe/CdSe and CdSe/ZnSe nanoparticles