The Application of Atomic Ab Initio Effective Potentials to the Cluster Calculations of an Octahedral Transition Metal Oxide and Flouride PDF Download
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Author: Winnie Wen-Cheng Chu Hsieh
Publisher:
ISBN:
Category :
Languages : en
Pages : 168
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Author: Winnie Wen-Cheng Chu Hsieh
Publisher:
ISBN:
Category :
Languages : en
Pages : 168
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Author:
Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 576
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Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 750
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Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 818
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Vols. for 1973- include the following subject areas: Biological sciences, Agriculture, Chemistry, Environmental sciences, Health sciences, Engineering, Mathematics and statistics, Earth sciences, Physics, Education, Psychology, Sociology, Anthropology, History, Law & political science, Business & economics, Geography & regional planning, Language & literature, Fine arts, Library & information science, Mass communications, Music, Philosophy and Religion.
Author: Petr Carsky
Publisher: Springer Science & Business Media
ISBN: 3642931405
Category : Science
Languages : en
Pages : 256
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Until recently quantum chemical ab initio calculations were re stricted to atoms and very small molecules. As late as in 1960 Allen l and Karo stated : "Almost all of our ab initio experience derives from diatomic LCAO calculations ••• N and we have found in the litera ture "approximately eighty calculations, three-fourths of which are for diatomic molecules ••• There are approximately twenty ab initio calculations for molecules with more than two atoms, but there is a decided dividing line between the existing diatomic and polyatomic wave functions. Confidence in the satisfactory evaluation of the many -center two-electron integrals is very much less than for the diatom ic case". Among the noted twenty calculations, SiH was the largest 4 molecule treated. In most cases a minimal basis set was used and the many-center two-electron integrals were calculated in an approximate way. Under these circumstances the ab initio calculations could hard ly provide useful chemical information. It is therefore no wonder that the dominating role in the field of chemical applications was played by semiempirical and empirical methods. The situation changed essentially in the next decade. The problem of many-center integrals was solved, efficient and sophisticated computer programs were devel oped, basis sets suitable for a given type of problem were suggested, and, meanwhile, a considerable amount of results has been accumulated which serve as a valuable comparative material. The progress was of course inseparable from the development and availability of computers.
Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 844
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Category : Aeronautics
Languages : en
Pages : 978
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Author: University Microfilms International
Publisher: Ann Arbor, Mich. : University Microfilms International
ISBN:
Category : Reference
Languages : en
Pages : 712
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Author: University Microfilms International
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 858
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Author:
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ISBN:
Category :
Languages : en
Pages : 7
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Vacancy formation and clustering significantly affect structural properties of transition-metal aluminides. Ab-initio quantum mechanical total-energy calculations using a full-potential linear combination of muffin-tin orbitals (LMTO) technique provide a convenient method of studying relevant characteristics such as changes in density of states, and charge redistribution around defects. Augmented with Hellmann-Feymann forces, LMTO allows calculations of relaxation geometries and relaxation energies. The authors have performed such calculations for vacancies and antisite substitutional point defects in Fe3Al with DO3 crystallographic structure. There are two limiting factors complicating calculations of defect formation energies directly from ab-initio calculations. The first is that a single defect, due to the lattice periodicity necessitated by the use of ab-initio total energy techniques, cannot be considered as an isolated defect, even in the maximum computable simulation cell. Unlike previous calculations, which did not find a dependency on the size of the simulation cell, the calculations have shown a significant difference in results for 32- and 16- atom cells. This difference provides information about vacancy clustering since it can be explained by a relatively small attractive interaction energy (approximately) 0.2 eV between two vacancies located in adjacent simulation cells and separated by the lattice constant distance (5.52 Å). By comparing the internal energies for two configurations of 30 atom cells (32 atom--2 vacancies), the authors were able to estimate that the attractive interaction between two vacancies could reach 1.2 eV. The second complication is the fact that chemical potentials of elements cannot be directly extracted from the total energy calculations for the compound. To deal with this problem, they considered two possible approximations and compared results, which were found to be quite similar for iron vacancies.
