{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/117712"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/117712","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Effective model Hamiltonian downfolded from first principles","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2023-04-12 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2023-04-12 without embargo terms","abstract_has_math":false,"creators":["Chang, Yueqing"],"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","Hughes, Taylor L","Cooper, S. Lance","Kahn, Yonatan F"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2022,"date_issued":"2022-12","date_published":"2022-12","updated_at":"2026-07-22T22:24:56Z","subjects":["Condensed matter physics","First-principles calculations","Downfolding"],"languages":["en","eng"],"rights":["Copyright 2022 Yueqing Chang"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/117712","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wagner, Lucas K","Hughes, Taylor L","Cooper, S. Lance","Kahn, Yonatan F"]},{"key":"dc:creator","label":"Author","values":["Chang, Yueqing"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2022-12","2022-08-26"]},{"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":["Condensed matter physics","First-principles calculations","Downfolding"]}]},{"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 2022 Yueqing Chang"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/117712"]}]},{"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 2023-04-12 without embargo terms","The student, Yueqing Chang, accepted the attached license on 2022-08-24 at 12:12.","The student, Yueqing Chang, submitted this Dissertation for approval on 2022-08-24 at 12:29.","This Dissertation was approved for publication on 2022-08-26 at 13:24.","DSpace SAF Submission Ingestion Package generated from Vireo submission #18470 on 2023-04-12 at 07:23:10","First-principles methods are tools for accurately predicting materials' electronic structures and properties. One application of highly accurate first-principles calculations is to derive effective models for describing the low-energy physics in many-electron systems. This dissertation is focused on deriving effective models from first principles for many-body systems using downfolding methods and improving the state-of-the-art downfolding framework. For applications to many-body systems, I explained the nanoscale electric field effect on monolayer 1T'-WTe2 electronic structure with layer-dependent spin-momentum locking, using a downfolded tight-binding Hamiltonian. To improve the downfolding methods, I generalized the density matrix downfolding method to incorporate the spin-orbit coupling so that both electron correlations and relativistic effects can be treated on equal footing. I also demonstrated in hydrogen chains that the density matrix downfolding method based on highly accurate first-principles many-body wave function techniques can detect emergent low- energy degrees of freedom. Another recent ongoing work is a comprehensive comparison between the widely used state-of-the-art downfolding method with highly accurate first-principles many-body wave function calculations. It will provide insights into how to correct the double counting error in density functional theory based downfolded models. Future directions of downfolding include systematically improving models using machine learning and potential applications in systems with multiple degrees of freedom. Downfolding from first principles will enhance our understanding of how the interplay between charges, spins, lattice, and their interactions give rise to the zoo of phases in correlated materials."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Effective model Hamiltonian downfolded from first principles"]}]}],"canonical_facts":{"dc:contributor":["Wagner, Lucas K","Hughes, Taylor L","Cooper, S. Lance","Kahn, Yonatan F"],"dc:creator":["Chang, Yueqing"],"dc:date":["2022-12","2022-08-26"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2023-04-12 without embargo terms","The student, Yueqing Chang, accepted the attached license on 2022-08-24 at 12:12.","The student, Yueqing Chang, submitted this Dissertation for approval on 2022-08-24 at 12:29.","This Dissertation was approved for publication on 2022-08-26 at 13:24.","DSpace SAF Submission Ingestion Package generated from Vireo submission #18470 on 2023-04-12 at 07:23:10","First-principles methods are tools for accurately predicting materials' electronic structures and properties. One application of highly accurate first-principles calculations is to derive effective models for describing the low-energy physics in many-electron systems. This dissertation is focused on deriving effective models from first principles for many-body systems using downfolding methods and improving the state-of-the-art downfolding framework. For applications to many-body systems, I explained the nanoscale electric field effect on monolayer 1T'-WTe2 electronic structure with layer-dependent spin-momentum locking, using a downfolded tight-binding Hamiltonian. To improve the downfolding methods, I generalized the density matrix downfolding method to incorporate the spin-orbit coupling so that both electron correlations and relativistic effects can be treated on equal footing. I also demonstrated in hydrogen chains that the density matrix downfolding method based on highly accurate first-principles many-body wave function techniques can detect emergent low- energy degrees of freedom. Another recent ongoing work is a comprehensive comparison between the widely used state-of-the-art downfolding method with highly accurate first-principles many-body wave function calculations. It will provide insights into how to correct the double counting error in density functional theory based downfolded models. Future directions of downfolding include systematically improving models using machine learning and potential applications in systems with multiple degrees of freedom. Downfolding from first principles will enhance our understanding of how the interplay between charges, spins, lattice, and their interactions give rise to the zoo of phases in correlated materials."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/117712"],"dc:language":["en","eng"],"dc:rights":["Copyright 2022 Yueqing Chang"],"dc:subject":["Condensed matter physics","First-principles calculations","Downfolding"],"dc:title":["Effective model Hamiltonian downfolded from first principles"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:24:56Z"}