An investigation into the phase stability of manganese oxide using quantum Monte Carlo and insights into materials prediction in the barium-ruthenium-sulfur phase space
Schiller, Joshua A
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https://hdl.handle.net/2142/89087
Description
Title
An investigation into the phase stability of manganese oxide using quantum Monte Carlo and insights into materials prediction in the barium-ruthenium-sulfur phase space
Author(s)
Schiller, Joshua A
Issue Date
2015-12-10
Director of Research (if dissertation) or Advisor (if thesis)
Ertekin, Elif
Department of Study
Mechanical Science & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
manganese oxide
mno
stability
materials prediction
barium
ruthenium
sulfur
quantum monte carlo (qmc)
discrete fourier transform (dft)
Abstract
We present an analysis of the polymorphic energy ordering and properties of the rock salt and zincblende structures of manganese oxide using fixed node dif- fusion Monte Carlo (DMC). Manganese oxide is a correlated, antiferromagnetic material that has proven to be challenging to model from first principles across a variety of approaches. Unlike conventional density functional theory and some hybrid functionals, fixed node diffusion Monte Carlo finds the rock salt structure to be more stable than the zincblende structure, and thus recovers the correct energy ordering. Analysis of the site-resolved charge fluctuations of the wave functions according to DMC and other electronic structure descriptions give insights into elements that are missing in other theories. While the calculated band gaps within DMC are in agreement with predictions that the zincblende polymorph has a lower band gap, the gaps themselves overestimate reported experimental values. Additionally, a preliminary analysis of a structure search in the barium-ruthenium-sulfur phase space using the evolutionary algorithm USPEX is presented. We identify find challenges to discovering new materials using an evolutionary algorithm as well as a potential new candidate structure, BaRu2S2 with space group 139.
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