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oai:dspace.mit.edu:1721.1/396372022-01-13T07:54:41Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022

Tomás A. Arias and John D. Joannopoulos. Ismail-Beigi, Sohrab, 1971- Massachusetts Institute of Technology. Dept. of Physics. Massachusetts Institute of Technology. Department of Physics 2007-11-16T14:36:31Z 2007-11-16T14:36:31Z 2000 2000 http://hdl.handle.net/1721.1/39637 47839618 Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2000. Includes bibliographical references (p. 159-165). We explore the use of ab initio, density-functional methods for the study of large-scale materials problems. Three examples are presented: (i) the interplay of surface and edge reconstructions in long silicon nanowires, where we examine the effects on electrical and mechanical properties; (ii) the calculation of solvation effects based on ab initio dielectric models, where we derive the dielectric treatment as a coarse-grained molecular description, apply our method to the hydrolysis reaction of methylene chloride, and examine simplifications to our ab initio method; and (iii) the study of screw dislocation cores in bcc molybdenum and tantalum, where we find core structures contrary to those commonly accepted and barriers to dislocation motion in better agreement with experiment. Methodologically, we present a new matrix-based, algebraic formalism for ab initio calculations which modularizes and isolates the roles played by the basis set, the energy functional, the algorithm used to achieve self-consistency, and the computational kernels. Development and implementation of new techniques amounts to derivation and transcription of algebraic expressions. Modularizing the computational kernels yields portable codes that are easily optimized and parallelized, and we present highly efficient kernels for scalar, shared, and distributed memory computers. We conclude with an analytical study of the spatial locality of the single-particle density matrix in solid-state systems. This locality reflects the localization of electronic states and is essential for real-space and O(N) methods. We derive new behavior for this spatial range contrary to previous proposals, and we verify our findings in model semiconductors, insulators, and metals. by Sohrab Ismail-Beigi. Ph.D. 165 p. eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Physics. New perspectives on ab initio calculation and physical insights gained through linkage to continuum theories Ab initio calculation and physical insights gained through linkage to continuum theories Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="8e9d6443-3e5c-47a6-a69e-113249a4dc79"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>New perspectives on ab initio calculation and physical insights gained through linkage to continuum theories</Title> <Subtitle>Ab initio calculation and physical insights gained through linkage to continuum theories</Subtitle> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2000</PublicationDate> <Authors> <Author> <DisplayName>Ismail-Beigi, Sohrab, 1971-</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Physics.</Keyword> <Abstract>We explore the use of ab initio, density-functional methods for the study of large-scale materials problems. Three examples are presented: (i) the interplay of surface and edge reconstructions in long silicon nanowires, where we examine the effects on electrical and mechanical properties; (ii) the calculation of solvation effects based on ab initio dielectric models, where we derive the dielectric treatment as a coarse-grained molecular description, apply our method to the hydrolysis reaction of methylene chloride, and examine simplifications to our ab initio method; and (iii) the study of screw dislocation cores in bcc molybdenum and tantalum, where we find core structures contrary to those commonly accepted and barriers to dislocation motion in better agreement with experiment. Methodologically, we present a new matrix-based, algebraic formalism for ab initio calculations which modularizes and isolates the roles played by the basis set, the energy functional, the algorithm used to achieve self-consistency, and the computational kernels. Development and implementation of new techniques amounts to derivation and transcription of algebraic expressions. Modularizing the computational kernels yields portable codes that are easily optimized and parallelized, and we present highly efficient kernels for scalar, shared, and distributed memory computers. We conclude with an analytical study of the spatial locality of the single-particle density matrix in solid-state systems. This locality reflects the localization of electronic states and is essential for real-space and O(N) methods. We derive new behavior for this spatial range contrary to previous proposals, and we verify our findings in model semiconductors, insulators, and metals.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>