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Density Functional Theory in Computational Materials Science
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is concerned to the application of first-principles self-consistent total-energy calculations within the density functional theory on different topics in materials science.

Crystallographic phase-transitions under high-pressure has been study for TiO2, FeI2, Fe3O4, Ti, the heavy alkali metals Cs and Rb, and C3N4. A new high-pressure polymorph of TiO2 has been discovered, this new polymorph has an orthorhombic OI (Pbca) crystal structure, which is predicted theoretically for the pressure range 50 to 100 GPa. Also, the crystal structures of Cs and Rb metals have been studied under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs-III and Rb-III phases. Thus, it is now certain that the famous isostructural phase transition in Cs is rather a new crystallographic phase transition.

The elastic properties of the new superconductor MgB2 and Al-doped MgB2 have been investigated. Values of all independent elastic constants (c11, c12, c13, c33, and c55) as well as bulk moduli in the a and c directions (Ba and Bc respectively) are predicted. Our analysis suggests that the high anisotropy of the calculated elastic moduli is a strong indication that MgB2 should be rather brittle. Al doping decreases the elastic anisotropy of MgB2 in the a and c directions, but, it will not change the brittle behaviour of the material considerably.

The three most relevant battery properties, namely average voltage, energy density and specific energy, as well as the electronic structure of the Li/LixMPO4 systems, where M is either Fe, Mn, or Co have been calculated. The mixing between Fe and Mn in these materials is also examined. Our calculated values for these properties are in good agreement with recent experimental values. Further insight is gained from the electronic density of states of these materials, through which conclusions about the physical properties of the various phases are made.

The electronic and magnetic properties of the dilute magnetic semiconductor Mn-doped ZnO has been calculated. We have found that for an Mn concentration of 5.6%, the ferromagnetic configuration is energetically stable in comparison to the antiferromgnetic one. A half-metallic electronic structure is calculated by the GGA approximation, where Mn ions are in a divalent state leading to a total magnetic moment of 5 μB per Mn atom.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 49
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1001
Keywords [en]
Physics, Density Functional Theory, High Pressure, Phase Transitions, Elastic Properties, Lithium Batteries, Dilute Magnetic Semiconductors
Keywords [sv]
Fysik
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-4496ISBN: 91-554-6016-X (print)OAI: oai:DiVA.org:uu-4496DiVA, id: diva2:164957
Public defence
2004-09-24, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-03-28Bibliographically approved
List of papers
1. Experimental and theoretical identification of a new high-pressure TiO2 polymorph
Open this publication in new window or tab >>Experimental and theoretical identification of a new high-pressure TiO2 polymorph
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2001 In: Phys. Rev. Lett., Vol. 87, p. 275501-1Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92002 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
2. Pressure-induced structural transformations in the Mott insulator FeI2
Open this publication in new window or tab >>Pressure-induced structural transformations in the Mott insulator FeI2
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2003 In: Phys. Rev. B, Vol. 68, p. 064105-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92003 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
3. The structure of the metallic high-pressure Fe3O4 polymorph: experimental and theoretical study
Open this publication in new window or tab >>The structure of the metallic high-pressure Fe3O4 polymorph: experimental and theoretical study
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2003 In: J. Phys.: Condens. Matter, Vol. 15, p. 7697-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92004 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
4. Titanium metal at high pressure: Synchrotron experiments and ab-initio calculations
Open this publication in new window or tab >>Titanium metal at high pressure: Synchrotron experiments and ab-initio calculations
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2004 In: Phys. Rev. B, Vol. 69, p. 184102-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92005 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
5. Structural phase transitions in heavy alkali metal under pressure
Open this publication in new window or tab >>Structural phase transitions in heavy alkali metal under pressure
2004 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 5, no 9, p. 1411-11415Article in journal (Refereed) Published
Abstract [en]

We performed a theoretical study of the crystal structures of cesium and rubidium under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs III and Rb III phases. The calculated transition pressures agree extremely well with the measured data. Thus, it is now certain that the famous isostructural phase transition in cesium is actually a new crystallographic phase transition. A d-orbital occupation number of about 0.52 is crucial for the occurrence of these complex structures.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92006 (URN)10.1002/cphc.200400292 (DOI)15499858 (PubMedID)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
6. Pressure effects on the structure and vibrations of β- and γ-C3N4
Open this publication in new window or tab >>Pressure effects on the structure and vibrations of β- and γ-C3N4
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2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 10, p. 104114-Article in journal (Refereed) Published
Abstract [en]

We present the results of an investigation on the pressure behavior of structural, bonding and vibrational properties of β- and γ-C3N4 phases. Emphasis is focused on the trends of the calculated properties along the A3N4 (A: C, Si, Ge) family. Geometry optimizations and electronic structure calculations are carried out in the framework of the local density functional theory using a planewave-pseudopotential scheme. The equilibrium cell geometry, the isothermal bulk modulus and its pressure derivatives have been evaluated for the two phases in a pressure range up to 400 GPa. The Bader’s Atoms in Molecules formalism is applied to characterize the chemical bonding and the atomic contributions to the bulk compressibility in β- and γ-A3N4 crystals. The calculated stability diagram reveals the occurrence of a hypothetical β-C3N4→γ-C3N4 phase transition around 370 GPa. Γ-point harmonic vibrational modes are computed at selected pressures within the density functional perturbation theory approach. In agreement with recent theoretical calculations, the comparison of the computed Raman vibrational frequencies with experimental estimations for β-C3N4 raises doubts on a previously reported synthesis of this structure. Pressure effects on the vibrational frequencies inform of a reduction of the P63∕m symmetry of the β phase at pressures around 60 GPa and contribute to look into the mechanical stability of the γ phase.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92007 (URN)10.1103/PhysRevB.70.104114 (DOI)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
7. Bonding and elastic properties of superconducting MgB2
Open this publication in new window or tab >>Bonding and elastic properties of superconducting MgB2
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2002 (English)In: Sol. Stat. Comm., Vol. 123, p. 257-Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92008 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-04-02Bibliographically approved
8. Elastic properties of Mg(1-x)AlxB2 from first principles theory
Open this publication in new window or tab >>Elastic properties of Mg(1-x)AlxB2 from first principles theory
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2004 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 29, p. 5241-5250Article in journal (Refereed) Published
Abstract [en]

Elastic properties of Mg(1−x)AlxB2 have been studied from first principles. The elastic constants (c11, c12, c13, c33 and c55) have been calculated, in the regime of x = 0 to 0.25. From these calculations the ratio between the bulk modulus and shear modulus (B/G) as well as the ratio between the two directional bulk moduli (Ba/Bc) have been evaluated. Our calculations show that the ratio Ba/Bc decreases monotonically as the aluminium content is increased, whereas the ratio B/G is well below the empirical ductility limit, 1.75, for all concentrations. In addition, we analyse the electronic structure and the nature of the chemical bonding, using the balanced crystal orbital overlap population (BCOOP) (Grechnev et al 2003 J. Phys.: Condens. Matter 15 7751) and the charge densities. Our analysis suggests that, while aluminium doping decreases the elastic anisotropy of MgB2 in the a and c directions, it will not change the brittle behaviour of the material considerably. 

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92691 (URN)10.1088/0953-8984/16/29/015 (DOI)
Available from: 2005-03-10 Created: 2005-03-10 Last updated: 2017-12-14Bibliographically approved
9. Calculation of surface stress for fcc transition metals
Open this publication in new window or tab >>Calculation of surface stress for fcc transition metals
2003 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 68, no 24, p. 245417-Article in journal (Refereed) Published
Abstract [en]

Using the density functional theory, formulated within the framework of the exact muffin-tin orbitals method, we have calculated the surface stress for the (111) free surfaces of the fcc 4d and 5d transition metals. Good agreement is obtained with the available ab initio data for Pd, Ir, and Au, while for Pt we predict a surface stress, which is about 33% lower compared to former theoretical results. The present surface stress values for the 4d and 5d fcc metals show the typical trend characteristic for the cohesive or surface energies of d series.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92010 (URN)10.1103/PhysRevB.68.245417 (DOI)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
10. A theoretical study of olivine LiMPO4 cathodes
Open this publication in new window or tab >>A theoretical study of olivine LiMPO4 cathodes
2004 In: Sol. Stat. Ionics, Vol. 167, p. 221-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92011 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
11. Electronic structure of MgxMo3S4 and related materials for green-rechargeable magnesium batteries
Open this publication in new window or tab >>Electronic structure of MgxMo3S4 and related materials for green-rechargeable magnesium batteries
Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-92012 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-13Bibliographically approved
12. Role of titanium in hydrogen desorption in crystalline sodium alanate
Open this publication in new window or tab >>Role of titanium in hydrogen desorption in crystalline sodium alanate
2005 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 25, article id 251913Article in journal (Refereed) Published
Abstract [en]

The role of Ti in improving the thermodynamics of hydrogen desorption in crystalline sodium alanate (NaAlH4) has been investigated by using the density functional theory. The total energy calculations reveal that Ti prefers to occupy the Na site over that of the Al site when the atomic energies are used as the reference. However, the use of the cohesive energies of Al, Na, and Ti leads to the Al site being the least unfavourable site. Irrespective of whether Ti occupies the Na or the Al site, the energy necessary to remove a hydrogen atom from Ti substituted sodium alanate is significantly lowered from that of the pure alanate. The understanding gained here may help in designing hydrogen storage materials suitable for industrial applications.

Keywords
hydrogen sorage, sodium alanate, electronic structure
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92013 (URN)10.1063/1.1953882 (DOI)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
13. Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO
Open this publication in new window or tab >>Ferromagnetism above room temperature in bulk and transparent thin films of Mn-doped ZnO
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2003 In: Nature Materials, Vol. 2, p. 673-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92014 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
14. Electroncic and magnetic propeties of Mn-doped ZnO from first-principles theory
Open this publication in new window or tab >>Electroncic and magnetic propeties of Mn-doped ZnO from first-principles theory
Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-92015 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-13Bibliographically approved
15. The electronic structure of Mn doped ZnO film from X-ray spectroscopy and DFT calculations
Open this publication in new window or tab >>The electronic structure of Mn doped ZnO film from X-ray spectroscopy and DFT calculations
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Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-92016 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2010-01-13Bibliographically approved
16. Optical properties of 4H-SiC
Open this publication in new window or tab >>Optical properties of 4H-SiC
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2002 In: J. Appl. Phys., Vol. 91, p. 2099-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92017 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
17. Electronic and optical properties of lead iodide
Open this publication in new window or tab >>Electronic and optical properties of lead iodide
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2002 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 92, p. 7219-Article in journal (Refereed) Published
Abstract [en]

The electronic properties and the optical absorption of lead iodide (PbI2) have been investigated experimentally by means of optical absorption and spectroscopic ellipsometry, and theoretically by a full-potential linear muffin-tin-orbital method. PbI2 has been recognized as a very promising detector material with a large technological applicability. Its band-gap energy as a function of temperature has also been measured by optical absorption. The temperature dependence has been fitted by two different relations, and a discussion of these fittings is given.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-92018 (URN)10.1063/1.1523145 (DOI)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
18. Spectroscopy studies of 4H-SiC
Open this publication in new window or tab >>Spectroscopy studies of 4H-SiC
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2002 In: Materials Research, Vol. 6, p. 43-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92019 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
19. Electronic and optical properties of γ-Al2O3 from ab-initio theory
Open this publication in new window or tab >>Electronic and optical properties of γ-Al2O3 from ab-initio theory
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2004 In: J. Phys.: Condens. Matter, Vol. 16, p. 2891-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-92020 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved
20. Electronic structure of a thermoelectric material: CsBi4Te6
Open this publication in new window or tab >>Electronic structure of a thermoelectric material: CsBi4Te6
In: Journal of Physics and Chemistry of SolidsArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-92021 (URN)
Available from: 2004-09-01 Created: 2004-09-01Bibliographically approved

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