New Density Functional Solution for Nondynamic and Strong Correlation

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Professor Jing Kong of Middle Tennessee State University (MTSU) is supported by an award from the Chemical Theory, Models and Computational Methods Program in the Chemistry Division to develop more accurate theoretical models for computer simulations of chemical processes. The rapidly increasing power of computers is making it ever more feasible to predict chemical reactivity through simulations. Simulations, in concert with experiment, can accelerate scientific discovery, but this is only possible if the underlying theoretical model is sufficiently accurate. Current prevailing models for electronic interactions are accurate for many, but not all, areas of chemistry. The physical effects they fail to predict accurately are important for accurate descriptions of catalysis, optical materials, and semiconducting and superconducting systems. The goal of this project is to build more accurate theoretical models at the fundamental level. The successful completion of this project expands the scope of quantum-mechanical based simulations and improves the quality and productivity of research in chemical and other physical sciences. The work is being done in the context of a new Computational Science program at MTSU, which is an interdisciplinary program that provides a unique opportunity to recruit students from non-chemistry backgrounds to pursue research in computational chemistry. MTSU has a student body with high percentages of undergraduate, minority and first-generation college students. Undergraduate students participate in computations that benchmark the activity of molecules or by coding parts of the methods. A new molecular modeling course for upper-level undergraduates is being developed and the results of this project can be used for the new course and other undergraduate course work.The strong correlation problem is the last frontier of Kohn-Sham Density Functional Theory (KS-DFT). It accounts for most of the failures of DFT for molecular and material systems. In this work, an accurate treatment of nondynamic/strong correlation is being developed based on single-determinant KS-DFT. The general-purpose functional treats strong correlation to the same degree of accuracy as current mainstream functionals treat weakly correlated molecular and extended systems. It is designed so that it can be implemented with sufficient efficiency for routine chemical applications with accurate treatment of both dynamic and nondynamic correlations. To achieve this goal, a general framework for nondynamic correlation is being developed based on the single-determinant KS scheme, subject to exact conditions. These conditions are specific for nondynamic correlation with degeneracy included and serve as guidelines for the development of a new model functional. Together with the development of an extensive benchmark database for nondynamic and strong correlation, and a new algorithm for efficient implementation, this functional significantly broadens the application of DFT to chemical and materials science problems involving electron correlation of all strengths. The software and the corresponding features produced in this project are made available through open source programs and open source distribution sites such that it can be used with other programs. The availability of the source code also facilitates others to develop new DFT methods. This research is expected to have a major impact on the nascent Computational Science PhD Program at MTSU, one of a handful in the country.