Electronic Structure Calculations of Materials by Auxiliary-Field Quantum Monte Carlo

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The PI and collaborators have developed an auxiliary-field quantum Monte Carlo (QMC) method that exhibits promising characteristics for improving the capabilities for electronic structure calculations of materials. The PI proposes to apply the new method to materials- specific problems, and continue its development. The project aims for: (i) accurate calculations of the ground state of solids, (ii) computation of generalized forces for geometry and structural optimizations in molecules and solids, (iii) calculations of excited-state properties with applications to prototypical semiconductors, and (iv) both ab initio and modelcalculations of strongly correlated materials.Intellectual merit. Understanding and predicting materials properties requires robust and reliable calculations at the most fundamental level. Often the desired effects originate from electron correlations, and small errors in their treatment can result in crucial and qualitative differences in the properties. Despite their tremendous success, standard computational electronic structure methods based on density functional theory are not always sufficient. Especially in strongly correlated materials, which are of particular theoretical and technological importance, they can sometimes lead to qualitatively incorrect results. QMC methods, which allow many-body calculations by stochastic sampling, are a promising alternative for treating correlated materials. Limitations in their capability, however, have thus far prevented wider applications of QMC to the many problems where accurate computations of electron correlations are critically needed. By exploiting opportunities that the new auxiliary-field framework presents, the PI will address some of these limitations.The PI's past experience and on-going research have ideally positioned him to effectively pursue the proposed project. Successful completion of this research will enhance the capabilities of first-principles computation in condensed matter, and advance the study of correlated materials. Further, the theoretical framework and technologies that are developed will also be relevant to nuclear physics, high-energy physics, and quantum chemistry, where similar approaches are used for non-perturbative calculations in many-body systems.Broader impacts. Building on past experience and success, the PI will continue to integrate research with education and outreach activities, by mentoring both undergraduate and graduate students in research, incorporating materials from this project into a new course, reaching out to minority students at Hampton University (HBCU), and fostering interdisciplinary collaboration in computational science education and research on campus. In the larger scientific community, the PI will continue to play an active role in training students, post-docs, and senior researchers through schools and workshops, developing software andtutorials for hands-on learning of new theoretical and computational approaches. In addition, the project will contribute to the build-up of computer codes for modeling and simulation of materials, by advancing QMC methodology to enable and facilitate its wide use, and by direct code contribution.***