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Density functional study of mono-vancacies in metals and austenitic steel alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Trough the following pages a comprehensive study of open structures will be shown, including mono-vacancy calculations and open surfaces. These are electronic structure calculations using density functional theory within the exact muffin tin method.

First I investigate the accuracy of five common density functional approximations for the theoretical description of the formation energy of mono-vacancies in three close  packed metals. Besides the local density approximation (LDA), I consider two generalized gradient approximation developed by Perdew and co-workers (PBE and PBEsol) and two gradient-level functionals obtained within the subsystem functional approach (AM05 and LAG). As test cases, I select aluminium, nickel and copper, all of them adopting the face centered cubic crystallographic structure.

This investigation is followed by a performance comparison of the three common gradient level exchange-correlation functionals for metallic bulk, surface and vacancy systems. I find that approximations which by construction give similar results for the jellium surface, show large deviations for realistic systems. The particular charge density and density gradient dependence of the exchange-correlation energy densities is shown to be the reason behind the obtained differences. Our findings confirm that both the global (total energy) and the local (energy density) behavior of the exchange-correlation functional should be monitored for a consistent functional design.

I also calculate the vacancy formation energies of paramagnetic face centered cubic (fcc) Fe-Cr-Ni alloys as a function of chemical composition. These alloys are well known model systems for low carbon austenitic stainless steels. The theoretical predictions obtained for homogeneous chemistry and relaxed nearest neighbor lattice sites are in line with the experimental observations. In particular, Ni is found to decrease and Cr increase the vacancy formation energy of the ternary system. The results are interpreted in terms of effective chemical potentials. The impact of vacancy on the local magnetic properties of austenitic steel alloys is also investigated.

I made a performance comparison of local density and generalized gradient level approach on substitutional defects in five light actinides. This is a complex test for high density calculations to check the weaknesses of the local density approximation against gradient level ones. I believe the existing other gradient level approaches fit our error bar in the obtained data and shows similar trends against the very limited number of experimental data. Based on our ab initio results, I predict that vacancies are more easily formed (more stable) in the fcc(bcc) lattice for U, Np and Pu and in the bcc(fcc) lattice for Th and Pa.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , vii, 50 p.
Keyword [en]
atomic defects, metalls, alloys, vacany, vacancy formation energy
National Category
Condensed Matter Physics Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-118792ISBN: 978-91-7501-671-9 (print)OAI: oai:DiVA.org:kth-118792DiVA: diva2:608398
Public defence
2013-03-26, F3, Linstedvagen 30, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note

QC 20130228

Available from: 2013-02-28 Created: 2013-02-27 Last updated: 2013-02-28Bibliographically approved
List of papers
1. Assessing common density functional approximations for the ab initio description of monovacancies in metals
Open this publication in new window or tab >>Assessing common density functional approximations for the ab initio description of monovacancies in metals
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 20Article in journal (Refereed) Published
Abstract [en]

Using the exact muffin-tin orbitals method, we investigate the accuracy of five common density functional approximations for the theoretical description of the formation energy of monovacancies in three close-packed metals. Besides the local density approximation (LDA), we consider two generalized gradient approximation developed by Perdew and co-workers (PBE and PBEsol) and two gradient-level functionals obtained within the subsystem functional approach (AM05 and LAG). As test cases, we select aluminum, nickel, and copper, all of them adopting the face centered cubic crystallographic structure. Our results show that, compared to the recommended experimental values, LDA is be the most reliable approximation for the vacancy formation energies in these metals. However, taking into account also the performances of the functionals for the equation of state changes the final verdict in favor of the generalized gradient approximations.

Keyword
vacancy-formation energies, electron-gas, 1st-principles calculations, transition-metals, aluminum, fcc, fe, impurities, perovskite, alloys
Identifiers
urn:nbn:se:kth:diva-19006 (URN)10.1103/PhysRevB.80.205121 (DOI)000272311400049 ()2-s2.0-77954720407 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Density functional theory of light actinides with substitutional point defects inface centered and body centered cubic descriptions
Open this publication in new window or tab >>Density functional theory of light actinides with substitutional point defects inface centered and body centered cubic descriptions
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-118796 (URN)
Note

QS 2013

Available from: 2013-02-27 Created: 2013-02-27 Last updated: 2013-02-28Bibliographically approved
3. Ab initio description of monovacancies in paramagnetic austenitic Fe-Cr-Ni alloys
Open this publication in new window or tab >>Ab initio description of monovacancies in paramagnetic austenitic Fe-Cr-Ni alloys
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 17, 174101- p.Article in journal (Refereed) Published
Abstract [en]

Using first-principles alloy theory, we calculate the vacancy formation energies of paramagnetic face-centered-cubic (fcc) Fe-Cr-Ni alloys as a function of chemical composition. These alloys are well-known model systems for low carbon austenitic stainless steels. The theoretical predictions obtained for homogeneous chemistry and relaxed nearest-neighbor lattice sites are in line with the experimental observations. In particular, Ni is found to decrease and Cr to increase the vacancy formation energy of the ternary system. The results are interpreted in terms of effective chemical potentials. The impact of vacancy on the local magnetic properties of austenitic steel alloys is also investigated.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-95245 (URN)10.1103/PhysRevB.85.174101 (DOI)000303387900001 ()2-s2.0-84861181395 (Scopus ID)
Funder
Swedish Research CouncilEU, European Research Council
Note
QC 20120522Available from: 2012-05-22 Created: 2012-05-21 Last updated: 2017-12-07Bibliographically approved
4. Density functional study of vacancies and surfaces in metals
Open this publication in new window or tab >>Density functional study of vacancies and surfaces in metals
2011 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 4, 045006- p.Article in journal (Refereed) Published
Abstract [en]

We compare the performances of three common gradient-level exchange-correlation functionals for metallic bulk, surface and vacancy systems. We find that approximations which, by construction, give similar results for the jellium surface, show large deviations for realistic systems. The particular charge density and density gradient dependence of the exchange-correlation energy densities are shown to be the reason behind the obtained differences. Our findings confirm that both the global (total energy) and the local (energy density) behavior of the exchange-correlation functional should be monitored for a consistent functional design.

National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-30524 (URN)10.1088/0953-8984/23/4/045006 (DOI)000286142800007 ()2-s2.0-78651486894 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20110304Available from: 2011-03-04 Created: 2011-02-28 Last updated: 2017-12-11Bibliographically approved

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