{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/108484"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/108484","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Understanding and extending the role of first-principles quantum Monte Carlo","abstract":"By providing a middle way between experiment and theory, first-principles electronic structure calculations provide a powerful tool for accelerating discovery in condensed matter physics. Computation provides a fast, cost-effective supplement to experiment, while simultaneously offering a greater level of flexibility than analytic theory. Indeed, first-principles electronic structure is already in use across a range of diverse fields, from photovoltaic research to pharmaceuticals. However, to make full use of first-principles calculations, we must understand the level of accuracy different techniques can offer, and how that accuracy varies across different quantities of interest. Because different techniques vary so widely in both their computational expense and methodological formulation, great care must be taken to understand when-and-where a particular approach should be applied. To this end, I report on several comparative studies I conducted that deepen our understanding of electronic structure methods in use today. First, I present a new technique for improving trial wavefunctions in quantum Monte Carlo (QMC) calculations. Trial wavefunction quality is one of the key limiting factors to the accuracy of QMC, and in this study I demonstrate one way to systematically overcome this barrier. I also present a study comparing the energetic accuracy of QMC to a group of over 20 methods for a collection of transition metal atoms and monoxides. This study was one of the largest of its kind yet undertaken, and one of the few to include numerically exact reference energies. I also report on several studies examining the success of different techniques in treating the electronic density. I demonstrate in one study the accuracy of QMC electronic densities relative to those provided by DFT for the perovskite BaTiO3, while in another study I analyze the relationship between errors in the total energy and in the density across a collection of small molecules. Finally, I show how QMC calculations can be used to construct accurate low-energy models for different systems. The results I present not only demonstrate the accuracy of QMC in a variety of domains, but carefully contextualize that accuracy relative to many of the other numerical techniques in use today.","abstract_html":"By providing a middle way between experiment and theory, first-principles electronic structure calculations provide a powerful tool for accelerating discovery in condensed matter physics. Computation provides a fast, cost-effective supplement to experiment, while simultaneously offering a greater level of flexibility than analytic theory. Indeed, first-principles electronic structure is already in use across a range of diverse fields, from photovoltaic research to pharmaceuticals. However, to make full use of first-principles calculations, we must understand the level of accuracy different techniques can offer, and how that accuracy varies across different quantities of interest. Because different techniques vary so widely in both their computational expense and methodological formulation, great care must be taken to understand when-and-where a particular approach should be applied. To this end, I report on several comparative studies I conducted that deepen our understanding of electronic structure methods in use today. First, I present a new technique for improving trial wavefunctions in quantum Monte Carlo (QMC) calculations. Trial wavefunction quality is one of the key limiting factors to the accuracy of QMC, and in this study I demonstrate one way to systematically overcome this barrier. I also present a study comparing the energetic accuracy of QMC to a group of over 20 methods for a collection of transition metal atoms and monoxides. This study was one of the largest of its kind yet undertaken, and one of the few to include numerically exact reference energies. I also report on several studies examining the success of different techniques in treating the electronic density. I demonstrate in one study the accuracy of QMC electronic densities relative to those provided by DFT for the perovskite BaTiO3, while in another study I analyze the relationship between errors in the total energy and in the density across a collection of small molecules. Finally, I show how QMC calculations can be used to construct accurate low-energy models for different systems. The results I present not only demonstrate the accuracy of QMC in a variety of domains, but carefully contextualize that accuracy relative to many of the other numerical techniques in use today.","abstract_has_math":false,"creators":["Williams, Kiel Troy"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Wagner, Lucas K","Dahmen, Karin","DeMarco, Brian","Eckstein, James"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020-10-07T20:59:50Z","date_published":"2020-10-07T20:59:50Z","updated_at":"2026-07-22T22:24:48Z","subjects":["Quantum electronic structure","computational condensed matter"],"languages":["en"],"rights":["Copyright 2020 Kiel Williams"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/108484","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wagner, Lucas K","Dahmen, Karin","DeMarco, Brian","Eckstein, James"]},{"key":"dc:creator","label":"Author","values":["Williams, Kiel Troy"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2020-10-07T20:59:50Z","2020-07-14","2020-08"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Quantum electronic structure","computational condensed matter"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2020 Kiel Williams"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/108484"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["By providing a middle way between experiment and theory, first-principles electronic structure calculations provide a powerful tool for accelerating discovery in condensed matter physics. Computation provides a fast, cost-effective supplement to experiment, while simultaneously offering a greater level of flexibility than analytic theory. Indeed, first-principles electronic structure is already in use across a range of diverse fields, from photovoltaic research to pharmaceuticals. However, to make full use of first-principles calculations, we must understand the level of accuracy different techniques can offer, and how that accuracy varies across different quantities of interest. Because different techniques vary so widely in both their computational expense and methodological formulation, great care must be taken to understand when-and-where a particular approach should be applied. To this end, I report on several comparative studies I conducted that deepen our understanding of electronic structure methods in use today. First, I present a new technique for improving trial wavefunctions in quantum Monte Carlo (QMC) calculations. Trial wavefunction quality is one of the key limiting factors to the accuracy of QMC, and in this study I demonstrate one way to systematically overcome this barrier. I also present a study comparing the energetic accuracy of QMC to a group of over 20 methods for a collection of transition metal atoms and monoxides. This study was one of the largest of its kind yet undertaken, and one of the few to include numerically exact reference energies. I also report on several studies examining the success of different techniques in treating the electronic density. I demonstrate in one study the accuracy of QMC electronic densities relative to those provided by DFT for the perovskite BaTiO3, while in another study I analyze the relationship between errors in the total energy and in the density across a collection of small molecules. Finally, I show how QMC calculations can be used to construct accurate low-energy models for different systems. The results I present not only demonstrate the accuracy of QMC in a variety of domains, but carefully contextualize that accuracy relative to many of the other numerical techniques in use today.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2020-10-02 without embargo terms","The student, Kiel Williams, accepted the attached license on 2020-07-13 at 14:40.","The student, Kiel Williams, submitted this Dissertation for approval on 2020-07-13 at 15:24.","This Dissertation was approved for publication on 2020-07-14 at 16:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15592 on 2020-10-02 at 15:13:13","Made available in DSpace on 2020-10-07T20:59:50Z (GMT). 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Computation provides a fast, cost-effective supplement to experiment, while simultaneously offering a greater level of flexibility than analytic theory. Indeed, first-principles electronic structure is already in use across a range of diverse fields, from photovoltaic research to pharmaceuticals. However, to make full use of first-principles calculations, we must understand the level of accuracy different techniques can offer, and how that accuracy varies across different quantities of interest. Because different techniques vary so widely in both their computational expense and methodological formulation, great care must be taken to understand when-and-where a particular approach should be applied. To this end, I report on several comparative studies I conducted that deepen our understanding of electronic structure methods in use today. First, I present a new technique for improving trial wavefunctions in quantum Monte Carlo (QMC) calculations. Trial wavefunction quality is one of the key limiting factors to the accuracy of QMC, and in this study I demonstrate one way to systematically overcome this barrier. I also present a study comparing the energetic accuracy of QMC to a group of over 20 methods for a collection of transition metal atoms and monoxides. This study was one of the largest of its kind yet undertaken, and one of the few to include numerically exact reference energies. I also report on several studies examining the success of different techniques in treating the electronic density. I demonstrate in one study the accuracy of QMC electronic densities relative to those provided by DFT for the perovskite BaTiO3, while in another study I analyze the relationship between errors in the total energy and in the density across a collection of small molecules. Finally, I show how QMC calculations can be used to construct accurate low-energy models for different systems. The results I present not only demonstrate the accuracy of QMC in a variety of domains, but carefully contextualize that accuracy relative to many of the other numerical techniques in use today.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2020-10-02 without embargo terms","The student, Kiel Williams, accepted the attached license on 2020-07-13 at 14:40.","The student, Kiel Williams, submitted this Dissertation for approval on 2020-07-13 at 15:24.","This Dissertation was approved for publication on 2020-07-14 at 16:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #15592 on 2020-10-02 at 15:13:13","Made available in DSpace on 2020-10-07T20:59:50Z (GMT). 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