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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2020)

This dissertation is an accumulation of my contribution to the fundamental understanding of ensemble Density Functional Theory and finite temperature Density Functional Theory, through the use of quantum model systems. Ensemble DFT is a time-independent method to extracting excitation energies, and provides a way to extract multiple excitations. Currently this is not possible with the common approximations used in time-dependent DFT. Chapter 3 of this thesis covers ensemble DFT and verifies an exact exchange approximation that can accurately capture multiple excitations using the Hubbard model. Finite temperature DFT is often incorrectly confused with ensemble DFT, and refers to DFT at non zero temperatures. Its value comes from its applications to warm dense matter simulations. The last three chapters of this dissertation contain several projects in the hopes of improving the understanding of finite temperature DFT. In particular it generalizes the PPLB derivative discontinuity model to finite temperatures, and discusses the construction of an exact finite temperature approximation. These contributions are done with the intention on enhancing warm dense simulations.

    Cover page: Developments in ensemble and finite temperature density functional theory using a model system
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2022)
    The dependence of ab initio many-body perturbation theory within the GW approximation on the eigensystem used in calculating quasiparticle corrections limits this method's predictive power. Here, we investigate the accuracy of the recently developed Wannier-localized optimally tuned screened range-separated hybrid (WOT-SRSH) functional as a generalized Kohn-Sham starting point for single-shot GW (G0W0) calculations for a range of semiconductors and insulators. Comparison to calculations based on well-established functionals, namely, PBE, PBE0, and HSE, as well as to self-consistent GW schemes and to experiment, shows that band gaps computed via G0W0@WOT-SRSH have a level of precision and accuracy that is comparable to that of more advanced methods such as quasiparticle self-consistent GW and eigenvalue self-consistent GW. We also find that G0W0@WOT-SRSH improves the description of states deeper in the valence band manifold. Finally, we show that G0W0@WOT-SRSH significantly reduces the sensitivity of computed band gaps to ambiguities in the underlying WOT-SRSH tuning procedure.
      Cover page: Optimally tuned starting point for single-shot GW calculations of solids
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2014)
      Understanding the peopling of the Americas remains an important and challenging question. Here, we present (14)C dates, and morphological, isotopic and genomic sequence data from two human skulls from the state of Minas Gerais, Brazil, part of one of the indigenous groups known as Botocudos. We find that their genomic ancestry is Polynesian, with no detectable Native American component. Radiocarbon analysis of the skulls shows that the individuals had died prior to the beginning of the 19th century. Our findings could either represent genomic evidence of Polynesians reaching South America during their Pacific expansion, or European-mediated transport.
        Cover page: Two ancient human genomes reveal Polynesian ancestry among the indigenous Botocudos of Brazil.
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2014)
        Understanding the peopling of the Americas remains an important and challenging question. Here, we present (14)C dates, and morphological, isotopic and genomic sequence data from two human skulls from the state of Minas Gerais, Brazil, part of one of the indigenous groups known as 'Botocudos'. We find that their genomic ancestry is Polynesian, with no detectable Native American component. Radiocarbon analysis of the skulls shows that the individuals had died prior to the beginning of the 19th century. Our findings could either represent genomic evidence of Polynesians reaching South America during their Pacific expansion, or European-mediated transport.
          Cover page: Two ancient human genomes reveal Polynesian ancestry among the indigenous Botocudos of BrazilCreative Commons 'BY-NC-ND' version 4.0 license
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