NSF/DMR-BSF: Density Functionals for Predictive Excited-State Calculations of Solids (NSF-BSF Application)

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research, and education to advance computational methods for predicting the properties of materials from fundamental scientific principles. The discovery and development of new materials for optoelectronic applications is significantly limited by a detailed understanding of how materials harvest light, transduce energy, and transport charge - all phenomena involving electronic excited states where the configuration of electrons leads to a higher energy than the lowest or ground state energy of the material. Existing computational methods are predictive for such processes, but they come at significant computational cost, and alternative approaches with similar accuracy would enable predictions for increasingly complex materials and for adapting such methods for materials discovery and design. This research project lays important groundwork toward the development of more efficient predictive theoretical frameworks that are complimentary to more computationally costly existing methods for electronic excited states in real materials. Central to this effort is mentoring of next-generation computational materials theorists at all age levels, with focus on active recruitment and promotion of women and other underrepresented-minority undergraduate and graduate students; and outreach through tours of local research facilities for undergraduate, elementary, and middle-school students – as well as educators – in the Bay area and beyond.TECHNICAL SUMMARYThis award supports theoretical and computational research, and education to advance computational methods for predicting the properties of materials. The electronic band structure is a fundamental property of crystalline matter. It serves as the basis for understanding charge transport properties of bulk materials. Moreover, it is a prerequisite for understanding optical properties of materials and for rationalizing the results of spectroscopic measurements. In materials and condensed matter physics, the formalism of choice for quantitative determination of the band structure has long been many-body perturbation theory (MBPT). This formalism has yielded excellent electronic structure predictions for many different classes of metals, semiconductors, and insulators. However, these predictions come at significant computational cost, and the ability to extract band structures from density functional theory (DFT), based on the single-electron energies and orbitals obtained from the solution of the Kohn-Sham equation, could alleviate this cost. This project involves a binational theoretical and computational collaboration to develop a robust framework for the first principles computational prediction of the quasiparticle band gaps, band structures, and optical spectra of complex solid-state materials with greater accuracy and efficiency than existing methodologies, by combining optimally-tuned range separated hybrid (OTRSH) density functionals with many-body perturbation theory. The PIs’ work has shown that OTRSH functionals lead to band structures and optical spectra for a broad class of molecular crystals and a set of group IV and III–V semiconductors and insulators, with the accuracy of leading-edge ab initio GW and GW-BSE approaches. Here, the PIs build on this success by advancing two important fronts simultaneously. First, the PIs will evaluate OTRSH as an effective starting point for GW and GW-BSE calculations for solids. Second, building on prior work, the PIs will explore routes to determine accurate DFT-OTRSH band structure and TDDFT-OTRSH optical properties without GW calculations. Once validated, the PIs will use OTRSH starting points to calculate the quasiparticle gap and band structure, as well as the linear absorption spectra, of an array of complex materials, including halide perovskites, important optoelectronic materials for which standard GW and GW-BSE methods have been demonstrated to be inadequate or inconsistent.The progress made thus far with OTRSH for band structure and optical spectra of solids is encouraging, as it suggests that it is in general possible to fix one parameter to the orientationally-averaged dielectric constant and then tune a single parameter – the range-separation parameter – to yield band structures and optical spectra in agreement with GW-BSE, partially or fully mitigating computational costs associated with MBPT. Given the quality of the OTRSH band structure with a single parameter, could OTRSH be an optimal starting point for GW and GW-BSE calculations of complex structurally and chemically heterogeneous systems? Additionally, it remains to be seen whether one can set this single parameter independent of GW-BSE calculations and experiment. Can it be predicted from materials properties in a computationally tractable manner, for isotropic and anisotropic materials alike? The aim of this project is to address these questions, and ultimately develop efficient approaches for understanding existing and predicting new excited-state phenomena in complex materials.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.