{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/125507"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/125507","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Advancing many-body methods for electronic structure calculations","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_has_math":false,"creators":["Wheeler, William A"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Materials Science & Engr","degree_department":null,"school":null,"contributors":["Wagner, Lucas K","Schleife, Andre","Shoemaker, Daniel P","Perry, Nicola H"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-05-24","date_published":"2024-05-24","updated_at":"2026-07-22T22:25:02Z","subjects":["Quantum Monte Carlo","Many-body Methods","Many-body Wave Functions","Electronic Structure","Excited States"],"languages":["en","eng"],"rights":["Copyright 2024 William Wheeler"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/125507","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wagner, Lucas K","Schleife, Andre","Shoemaker, Daniel P","Perry, Nicola H"]},{"key":"dc:creator","label":"Author","values":["Wheeler, William A"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2024-05-24","2024-08"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science & Engr"]},{"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 Monte Carlo","Many-body Methods","Many-body Wave Functions","Electronic Structure","Excited States"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2024 William Wheeler"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/125507"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, William Wheeler, accepted the attached license on 2024-05-17 at 15:16.","The student, William Wheeler, submitted this Dissertation for approval on 2024-05-17 at 15:37.","This Dissertation was approved for publication on 2024-05-24 at 09:14.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20802 on 2025-02-04 at 21:03:20","Ab initio calculations of materials complement experimental techniques by enabling prediction of properties of materials, as well as accessing quantities that are difficult or impossible to measure in the lab. In strongly correlated materials, properties depend strongly on the coordination of many electrons together, requiring many-body descriptions that explicitly capture electron interactions. This dissertation advances the methods available for ab initio many-body calculations in several areas. In this work, I analyze the capabilities and limitations of a new formula for calculating bulk electric quadrupole moments of many-body wave functions. Interpreting the quadrupole as the result of dipoles flowing through the material highlights subtleties of defining this quantity. With the aim of streamlining development of new formulas and algorithms, I introduce PyQMC, a new implementation of quantum Monte Carlo (QMC) in Python. PyQMC reduces the human time in algorithm development and workflow design through a modular, easy-to-modify codebase. The capabilities of PyQMC are brought to my next project, characterizing spin fluctuations in the ground state of unconventional superconductor CaCuO2. Multi- determinant QMC trial functions are shown to capture spin fluctuations in the undoped parent compound and orbital optimization is demonstrated to be viable on these wave functions, establishing the basis for analyzing spin fluctuations in the less understood doped material. Moving towards excited states, I analyze an algorithm for calculating excited states using many-body wave function based techniques. The approach introduces the first variational principle for an ensemble of trial states, where an objective function is minimized only by the ensemble of the lowest N eigenstates. My work opens the path towards constructing an effective model of the cuprates at QMC level accuracy, which requires high-accuracy ground and excited states and reliable characterization of the spin and charge correlations in the materials. The tools and methods I present will transfer to accurate characterization of other systems and support future efforts to understand and model strongly correlated materials."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Advancing many-body methods for electronic structure calculations"]}]}],"canonical_facts":{"dc:contributor":["Wagner, Lucas K","Schleife, Andre","Shoemaker, Daniel P","Perry, Nicola H"],"dc:creator":["Wheeler, William A"],"dc:date":["2024-05-24","2024-08"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, William Wheeler, accepted the attached license on 2024-05-17 at 15:16.","The student, William Wheeler, submitted this Dissertation for approval on 2024-05-17 at 15:37.","This Dissertation was approved for publication on 2024-05-24 at 09:14.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20802 on 2025-02-04 at 21:03:20","Ab initio calculations of materials complement experimental techniques by enabling prediction of properties of materials, as well as accessing quantities that are difficult or impossible to measure in the lab. In strongly correlated materials, properties depend strongly on the coordination of many electrons together, requiring many-body descriptions that explicitly capture electron interactions. This dissertation advances the methods available for ab initio many-body calculations in several areas. In this work, I analyze the capabilities and limitations of a new formula for calculating bulk electric quadrupole moments of many-body wave functions. Interpreting the quadrupole as the result of dipoles flowing through the material highlights subtleties of defining this quantity. With the aim of streamlining development of new formulas and algorithms, I introduce PyQMC, a new implementation of quantum Monte Carlo (QMC) in Python. PyQMC reduces the human time in algorithm development and workflow design through a modular, easy-to-modify codebase. The capabilities of PyQMC are brought to my next project, characterizing spin fluctuations in the ground state of unconventional superconductor CaCuO2. Multi- determinant QMC trial functions are shown to capture spin fluctuations in the undoped parent compound and orbital optimization is demonstrated to be viable on these wave functions, establishing the basis for analyzing spin fluctuations in the less understood doped material. Moving towards excited states, I analyze an algorithm for calculating excited states using many-body wave function based techniques. The approach introduces the first variational principle for an ensemble of trial states, where an objective function is minimized only by the ensemble of the lowest N eigenstates. My work opens the path towards constructing an effective model of the cuprates at QMC level accuracy, which requires high-accuracy ground and excited states and reliable characterization of the spin and charge correlations in the materials. The tools and methods I present will transfer to accurate characterization of other systems and support future efforts to understand and model strongly correlated materials."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/125507"],"dc:language":["en","eng"],"dc:rights":["Copyright 2024 William Wheeler"],"dc:subject":["Quantum Monte Carlo","Many-body Methods","Many-body Wave Functions","Electronic Structure","Excited States"],"dc:title":["Advancing many-body methods for electronic structure calculations"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Materials Science & Engr"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:02Z"}