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Effects of disorder in metallic systems from First-Principles calculations
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, quantum-mechanical calculations within density-functional theory on metallic systems are presented. The overarching goal has been to investigate effects of disorder. In particular, one of the properties investigated is the bindingenergy shifts for core electrons in binary alloys using different theoretical methods. These methods are compared with each other and with experimental results. One such method, the so-called Slater-Janak transition state method relies on the assumption that the single-particle eigenvalues within density-functional theory are linear functions of their respective occupation number. This assumption is investigated and it is found that while the eigenvalues to a first approximation show linear behavior, there are also nonlinearities which can influence the core-level binding energy shifts.

Another area of investigation has been iron based alloys at pressures corresponding to those in the Earth’s inner core. This has been done for the hexagonal close packed and face entered cubic structures. The effects of alloying iron with magnesium and nickel on the equation of state as well on the elastic properties have been investigated. The calculations have shown that the hexagonal close packed structure in FeNi is more isotropic than the face-centered cubic structure, and that adding Mg to Fe has a large impact on the elastic properties.

Finally, the effects of disorder due to thermal motion of the atoms have been investigated through ab-initio molecular dynamics simulations. Within the limits of this method and the setup, it is found that the face-centered cubic structure of molybdenum can be dynamically stabilized at high temperature, leading to a metastable structure, on the average. The dynamical stabilization of face-centered cubic molybdenum also rendered it possible to accurately calculate the lattice stability relative to the body-centered cubic phase. Inclusion of temperature effects for the lattice stability using ab-initio molecular dynamics simulations resolves the disagreement between ab-initio calculations and thermochemical methods.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 126 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1299
Keyword [en]
Iron, Nickel, Magnesium, Manganese, Molybdenum, Zirconium, Elastic Constants, High pressure, Earth's core, Density-functional theory, Ab-initio, First-Principles, Core-level shifts, Molecular Dynamics, Phonons, Dynamical Instability
National Category
Condensed Matter Physics Other Physics Topics
Identifiers
URN: urn:nbn:se:liu:diva-53584ISBN: 978-91-7393-445-9 (print)OAI: oai:DiVA.org:liu-53584DiVA: diva2:289541
Public defence
2010-03-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-02-11 Created: 2010-01-25 Last updated: 2010-03-29Bibliographically approved
List of papers
1. Core-level shifts in fcc random alloys: A first-principles approach
Open this publication in new window or tab >>Core-level shifts in fcc random alloys: A first-principles approach
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2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 6, 064203- p.Article in journal (Refereed) Published
Abstract [en]

First-principles theoretical calculations of the core-level binding-energy shift (CLS) for eight binary face-centered-cubic (fcc) disordered alloys, CuPd, AgPd, CuNi, NiPd, CuAu, PdAu, CuPt, and NiPt, are carried out within density-functional theory (DFT) using the coherent potential approximation. The shifts of the Cu and Ni 2p3∕2, Ag and Pd 3d5∕2, and Pt and Au 4f7∕2 core levels are calculated according to the complete screening picture, which includes both initial-state (core-electron energy eigenvalue) and final-state (core-hole screening) effects in the same scheme. The results are compared with available experimental data, and the agreement is shown to be good. The CLSs are analyzed in terms of initial- and final-state effects. We also compare the complete screening picture with the CLS obtained by the transition-state method, and find very good agreement between these two alternative approaches for the calculations within the DFT. In addition the sensitivity of the CLS to relativistic and magnetic effects is studied.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-12565 (URN)10.1103/PhysRevB.72.064203 (DOI)
Note

Original publication: W. Olovsson, C. Göransson, L. V. Pourovskii, B. Johansson and I. A. Abrikosov, Core-level shifts in fcc random alloys: A first-principles approach, 2005, Physical Review B, (72), 064203. Copyright: The America Physical Society, http://prb.aps.org/

Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
2. Numerical investigation of the validity of the Slater-Janak transition-state model in metallic systems
Open this publication in new window or tab >>Numerical investigation of the validity of the Slater-Janak transition-state model in metallic systems
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 13Article in journal (Refereed) Published
Abstract [en]

According to the so-called Janak’s theorem, the eigenstates of the Kohn-Sham Hamiltonian are given by the derivative of the total energy with respect to the occupation numbers of the corresponding one-electron states. The linear dependence of the Kohn-Sham eigenvalues on the occupation numbers is often assumed in order to use the Janak’s theorem in applications, for instance, in calculations of the core-level shifts in materials by means of the Slater-Janak transition state model. In this work first-principles density-functional theory calculations using noninteger occupation numbers for different core states in 24 different random alloy systems were carried out in order to verify the assumptions of linearity. It is found that, to a first approximation, the Kohn-Sham eigenvalues show a linear behavior as a function of the occupation numbers. However, it is also found that deviations from linearity have observable effects on the core-level shifts for some systems. A way to reduce the error with minimal increase of computational efforts is suggested.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12559 (URN)10.1103/PhysRevB.72.134203 (DOI)
Note

Original publication: C. Göransson, W. Olovsson and I. A. Abrikosov, Numerical investigation of the validity of the Slater-Janak transition-state model in metallic systems, 2005, Physical Review B, (72), 134203. Copyright: The America Physical Society, http://prb.aps.org/

Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
3. Core-level shifts in complex metallic systems from first principle
Open this publication in new window or tab >>Core-level shifts in complex metallic systems from first principle
2006 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 11, 2447-2464 p.Article in journal (Refereed) Published
Abstract [en]

We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations.

Place, publisher, year, edition, pages
Wiley, 2006
Keyword
71.15.-m, 71.23.-k, 79.20.Fv, 79.60.Dp, 79.60.Ht, 79.60.Jv
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-37239 (URN)10.1002/pssb.200642165 (DOI)34061 (Local ID)34061 (Archive number)34061 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
4. Elastic properties of Fe–Mn random alloys studied by ab initio calculations
Open this publication in new window or tab >>Elastic properties of Fe–Mn random alloys studied by ab initio calculations
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2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 19, 191904- p.Article in journal (Refereed) Published
Abstract [en]

We have studied the influence of the Mn content on the elastic properties of Fe–Mn random alloys (space group of Fmm) using ab initio calculations. The magnetic effects in Fe–Mn alloys have a strong influence on the elastic properties, even above the Néel temperature. As the Mn content is increased from 5  to  40  at.  %, the C44 elastic constant is unaffected, while C11 and C12 decrease. This behavior can be understood based on the magnetovolume effect which softens the lattice. Since the amplitude of local magnetic moments is less sensitive to volume conserving distortions, the softening is not present during shearing.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12567 (URN)10.1063/1.2807677 (DOI)
Note
Original publication: Denis Music, Tetsuya Takahashi, Levente Vitos, Christian Asker, Igor A. Abrikosov and Jochen M. Schneider, Elastic properties of Fe–Mn random alloys studied by ab initio calculations, 2007, Applied Physics Letters, (91), 191904. Copyright: The America Institute of Physics, http://www.aip.org/ Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
5. First-principles solution to the problem of Mo lattice stability
Open this publication in new window or tab >>First-principles solution to the problem of Mo lattice stability
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 220102(R)Article in journal (Refereed) Published
Abstract [en]

The energy differences between the ground state body-centered structure and closed-packed face-centered structure for transition metals in the middle of the series show unusually large disagreements when they are obtained by the thermochemical approach based on the analysis of experimental data or by first-principles electronic structure calculations. Considering a typical example, the lattice stability of Mo, we present a solution to this long-standing problem. We carry out ab initio molecular dynamics simulations for the two phases at high temperature and show that the configurational energy difference approaches the value derived by means of the thermochemical approach. The main contribution to the effect comes from the modification of the canonical band structure due to anharmonic thermal motion at high temperature.

 

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-12560 (URN)10.1103/PhysRevB.77.220102 (DOI)
Note
Original publication: C. Asker, A. B. Belonoshko, A. S. Mikhaylushkin and I. A. Abrikosov, First-principles solution to the problem of Mo lattice stability, 2008, Physical Review B, (77), 220102(R). Copyright: The America Physical Society, http://prb.aps.org/Available from: 2008-09-15 Created: 2008-09-15 Last updated: 2017-12-14
6. Elastic constants and anisotropy in FeNi alloys at high pressures from first-principles calculations
Open this publication in new window or tab >>Elastic constants and anisotropy in FeNi alloys at high pressures from first-principles calculations
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 21, 214112- p.Article in journal (Refereed) Published
Abstract [en]

The single-crystal and polycrystalline elastic constants and the elastic anisotropy in face-centered cubic and hexagonal close-packed FeNi alloys have been investigated at ultrahigh pressures by means of first-principles calculations using the exact muffin-tin orbitals method and the coherent-potential approximation. Comparisons with earlier calculations for pure Fe and experimental results are presented and discussed. We show that Ni alloying into Fe increases slightly the density and has very little effect on bulk moduli. Moreover, the relative decrease in c(44) elastic constant is much stronger in the hcp phase than in the fcc one. It is found that the elastic anisotropy is higher for face-centered cubic than for the hexagonal close-packed structure of FeNi, even though the face-centered cubic phase has a higher degree of symmetry. The anisotropy in face-centered cubic structure decreases with increasing nickel concentration while a very weak increase is observed for the hexagonal close-packed structure.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-20159 (URN)10.1103/PhysRevB.79.214112 (DOI)
Available from: 2009-09-01 Created: 2009-08-31 Last updated: 2017-12-13
7. Equation of state and elastic properties of face-centered cubic FeMg alloy at ultrahigh pressures from first-principles
Open this publication in new window or tab >>Equation of state and elastic properties of face-centered cubic FeMg alloy at ultrahigh pressures from first-principles
2010 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 293, no 1-2, 130-134 p.Article in journal (Refereed) Published
Abstract [en]

We have ca1culated the equation of state and elastic properties of face-centered cubic Fe and Fe-rich FeMg alloy at ultrahigh pressures from first principles using the Exact Muffin-Tin Orbitals method. The results show that adding Mg into Fe influences strongly the equation of state, and cause a large degree of softening of the elastic constants, even at concentrations as small as 1-2 at. %. Moreover, the e1astic anisotropy increases, and the effect is higher at higher pressures.

Keyword
Ab initio, Elasticity, equation of state, iron, magnesium, Earths inner core, Pressure
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-53906 (URN)10.1016/j.epsl.2010.02.032 (DOI)000277217100013 ()
Note
Original Publication: Christian Asker, U. Kargén, L. Dubrovinsky and Igor Abrikosov, Equation of state and elastic properties of face-centered cubic FeMg alloy at ultrahigh pressures from first-principles, 2010, Earth and Planetary Science Letters, (293), 1-2, 130-134. http://dx.doi.org/10.1016/j.epsl.2010.02.032 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-02-11 Created: 2010-02-11 Last updated: 2017-12-12
8. Electronic and atomic structure of Mo from high-temperature molecular dynamics simulations
Open this publication in new window or tab >>Electronic and atomic structure of Mo from high-temperature molecular dynamics simulations
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

By means of ab initio molecular dynamics (AIMD) simulations we carry out a detailed stdly of the electronic and atomic structure of Mo upon the thermal stabilization of its dynamically unstable face-centered cubic (fcc) phase, Wc calculate how the atomic positions, radial distribution function, and the ei<xtronic density of states of fcc Mo evolve with temperature. The results are compared with those for dynamically stable body-centered cubic (bcc) phase of Mo, as well as with bcc Zr, which is dynamically unstable at T = OK, but (in contrast to fcc Mo) becomes thermodynamically stable at high temperature, In particular, wc emphasize the difference between the local positions of atoms in the simulation boxes at a particular step of AIMD simulation and the average positions, around which the atoms vibrate, and show that the former are solcly responsible for the electronic properties of the material. WE observe that while the average atomic positions in fcc Mo correspond perfectly to the ideal structure at high temperature, the electronic structure of the metal calculated from AIMD differs substantially from the canonical shape of the density of states for the ideal fcc crystaL From a comparison of our results obtained for fcc Mo arid bcc Zr, we advocate the use of the electronic structure calculations, complemented with studies of radial distribution functions, as a sensitive test of a degree of the temperature induced stabilization of phases, which are dynamically unstable at T = OK.

Identifiers
urn:nbn:se:liu:diva-53779 (URN)
Available from: 2010-02-03 Created: 2010-02-03 Last updated: 2010-02-11

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