Weitao Yang of Duke University is supported by an award from the Theoretical and Computational Chemistry program for research on the development of density functional theory for large systems. In prior work supported by NSF the PI developed an important new functional known as the Mori-Cohen-Yang (MCY) functional and is now making certain corrections and enhancements to it. The first step involves the development of a way to model the adiabatic connection in the coupling constant dependence. Different models and various density functional approximations are being explored. The research also aims to develop functionals of the Kohn-Sham potential using many-electron theory to build these functionals. Further functional development is being explored for the van der Waals interaction and testing of new orbital functionals are being conducted for the calculation of excitation energies through TDDFT and other methods. This work is having a very broad impact on fields in which density functional theory is used for modeling, such as biology, materials science, physics and engineering.