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Towards Large-Scale Quantum Accuracy Materials Simulations

Vikram Gavini, University of Michigan

Electronic structure calculations, especially those using density functional theory (DFT), have been very useful in understanding and predicting a wide range of materials properties. The importance of DFT calculations to engineering and physical sciences is evident from the fact that ~20% of computational resources on some of the world’s largest public supercomputers are devoted to DFT calculations. Despite the wide adoption of DFT, and the tremendous progress in theory and numerical methods over the decades, the following challenges remain. Firstly, the state-of-the-art implementations of DFT suffer from cell-size and geometry limitations, with the widely used codes in solid state physics being limited to periodic geometries and typical simulation domains containing a few hundred atoms. This limits the complexity of materials systems that can be treated using DFT calculations. Secondly, there are many materials systems (such as strongly-correlated systems) where the widely used model exchange-correlation functionals in DFT, which account for the many-body quantum mechanical interactions between electrons, are inaccurate. Addressing these challenges will enable large-scale quantum-accuracy DFT calculations, and will significantly advance our ab initio modeling capabilities to treat complex materials systems.
This talk will discuss our recent advances towards addressing the aforementioned challenges. In particular, the development of computational methods and numerical algorithms for conducting fast and accurate large-scale DFT calculations using adaptive finite-element discretization will be presented, which form the basis for the recently released DFT-FE open-source code. The computational efficiency, scalability and performance of DFT-FE will be presented, which demonstrates a significant outperformance of widely used plane-wave DFT codes. Some recent studies that highlight the capabilities of DFT-FE will be presented, which include: (i) studies on dislocation energetics in Magnesium; (ii) understanding the electronic structure underpinnings of electron transport in DNA molecules; (iii) computation of the spin Hamiltonian parameters that govern the coherence times in spin qubits. In addressing the second challenge, our recent breakthrough in accurately solving the inverse DFT problem will be presented, which has enabled the computation of exact exchange-correlation potentials for polyatomic systems. Ongoing efforts on using the exact exchange-correlation potentials to develop a data-driven approach for improving the exchange-correlation functional description in DFT will be discussed.
This is joint work with Sambit Das (U. Michigan), Bikash Kanungo (U. Michigan) and Phani Motamarri (IISc).