Development and Applications of Density Functional Methods for Large Systems

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With support from the Chemical Theory, Models and Computational Methods (CTMC) program in the Division of Chemistry, Professor Weitao Yang of Duke University will develop methods in density functional theory for accurate prediction of energy, charge distributions and optical spectroscopy for large and complex systems. The proposed developments should have broad application in a wide range of computational modeling in biology, chemistry, physics, engineering and nano- science and technology. Yang and his research group will disseminate the knowledge and technology gained through these studies through publication of original research work and the public distribution of software packages. The proposed work will contribute to the development of human resources, for the future generation of theoretical and computational chemistry researchers, and will broaden participation in science, technology, engineering and mathematics through Project SEED. Under this award, Weitao Yang and his research group will develop corrections to common density functional approximations to satisfy key constraints on fractional charges and fractional spins. Commonly used approximate functionals have major systematic errors: the delocalization error, as the deviation from the exact linearity condition for fractional charges in a convex behavior, and the strong/static correlation error, as the violation of the constancy condition for fractional spins. Necessary conditions for overcoming these errors have been expressed in terms of fractional charges, fractional spins and their combination. Outstanding challenges in density functional theory remain to satisfy these conditions and overcome the associated systematic errors. Yang and his group will focus on the following three directions: (1) eliminating delocalization error with localized orbital scaling correction, (2) exploring the fundamental principles of obtaining excited state energetic information from ground state density functional theory calculations, and (3) reducing static correction error with localized orbital scaling correction and with multireference density functional theory based on the linear response theory. The broad scientific impact of the work will be enhanced as the Yang team plans to make the computational software developed in this work freely available to the scientific community.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.