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Development and applications of theoretical algorithms for simulations of materials at extreme conditions
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Materials at extreme conditions exhibit properties that differ substantially from ambient conditions. High pressure and high temperature expose anharmonic, non-linear behavior, and can provoke phase transitions among other effects. Experimental setups to study that sort of effects are typically costly and experiments themselves are laborious. It is common to apply theoretical techniques in order to provide a road-map for experimental research. In this thesis I cover computational algorithms based on first-principles calculations for high-temperature and high-pressure conditions. The two thoroughly described algorithms are: 1) the free energy studies using temperature-dependent effective potential method (TDEP), and 2) a higher-order elastic constants calculation procedure. The algorithms are described in an easy to follow manner with motivation for every step covered.

The Free energy calculation algorithm is demonstrated with applications to hexagonal close-packed Iron at the conditions close to the inner Earth Core’s. The algorithm of elastic constants calculation is demonstrated with application to Molybdenum, Tantalum, and Niobium. Other projects included in the thesis are the study of effects of van der Waals corrections on the graphite and diamond equations of state.

Abstract [sv]

Material vid extrema förhållanden uppvisar egenskaper som skiljer sig avsevärt från omgivningsförhållanden. Högt tryck och hög temperatur exponera anharmonicity, icke-linjärt beteende, och kan framkalla fasövergångar bland andra effekter. Experimentella uppställningar för att studera denna typ av effekter är vanligtvis dyra och experiment själva är mödosam. Det är vanligt att tillämpa teoretiska metoder för att ge en färdplan för experimentell forskning. I denna avhandling täcker jag beräkningsalgoritmer baserat på första principer beräkningar för hög temperatur och högt tryck. De två grundligt beskrivna algoritmer är: 1) den fria energin studier med temperaturberoende effektiv potentiell metod (TDEP), och 2) en högre ordning elastiska konstantberäkningsproceduren. Algoritmerna beskrivs i en lätt att följa sätt med motivation för varje steg som omfattas.

Den fria energiberäkningsalgoritm visas med program till hexagonal tätpackad järn på villkoren nära jordens inre kärna. Algoritmen av elastiska konstanter beräkning demonstreras med tillämpning till molybden, tantal, och niob. Andra projekt som ingår i avhandlingen är effekterna av van der Waals-korrigeringar på tillståndsekvation och elastiska konstanter i grafit och diamant.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , p. 85
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1844
National Category
Condensed Matter Physics Other Physics Topics Atom and Molecular Physics and Optics Other Materials Engineering Theoretical Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-136447DOI: 10.3384/diss.diva-136447ISBN: 9789176855430 (print)OAI: oai:DiVA.org:liu-136447DiVA, id: diva2:1087791
Public defence
2017-04-28, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-04-21Bibliographically approved
List of papers
1. Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method
Open this publication in new window or tab >>Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method
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2016 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 120, no 43, p. 8761-8768Article in journal (Refereed) Published
Abstract [en]

Free energy calculations at finite temperature based on ab initio molecular dynamics (AIMD) simulations have become possible, but they are still highly computationally demanding. Besides, achieving simultaneously high accuracy of the calculated results and efficiency of the computational algorithm is still a challenge. In this work we describe an efficient algorithm to determine accurate free energies of solids in simulations using the recently proposed temperature-dependent effective potential method (TDEP). We provide a detailed analysis of numerical approximations employed in the TDEP algorithm. We show that for a model system considered in this work, hcp Fe, the obtained thermal equation of state at 2000 K is in excellent agreement with the results of standard calculations within the quasiharmonic approximation.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:liu:diva-132993 (URN)10.1021/acs.jpca.6b08633 (DOI)000387198600028 ()27700093 (PubMedID)
Note

Funding Agencies|Swedish Foundation for Strategic Research (SSF) program SRL [10-0026]; Swedish Research Council (VR) [2015-04391, 2014-4750, 637-2013-7296]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; PRACE-2IP project [FP7 RI-283493]

Available from: 2016-12-09 Created: 2016-12-07 Last updated: 2017-04-24Bibliographically approved
2. Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
Open this publication in new window or tab >>Theoretical description of pressure-induced phase transitions: a case study of Ti-V alloys
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2015 (English)In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 35, no 1, p. 42-48Article in journal (Refereed) Published
Abstract [en]

We discuss theoretical description of pressure-induced phase transitions by means of first-principles calculations in the framework of density functional theory. We illustrate applications of theoretical tools that allow one to take into account configurational and vibrational disorders, considering Ti-V alloys as a model system. The universality of the first-principles theory allows us to apply it in studies of different phenomena that occur in the Ti-V system upon compression. Besides the transitions between different crystal structures, we discuss isostructural transitions in bcc Ti-V alloys. Moreover, we present arguments for possible electronic transitions in this system, which may explain peculiar behaviour of elastic properties of V upon compression.

Place, publisher, year, edition, pages
Taylor andamp; Francis: STM, Behavioural Science and Public Health Titles, 2015
Keywords
phase stability; first-principles calculations; Ti-V alloys; high pressure
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-114586 (URN)10.1080/08957959.2014.992896 (DOI)000348672100007 ()
Note

Funding Agencies|Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; SSF [SRL 10-0026]; Russian Foundation for Basic Researches [13-02-00606a]; Tomsk State University Academic D.I. Mendeleev Fund Program; Program of Fundamental Research of State Academies of Sciences

Available from: 2015-02-27 Created: 2015-02-26 Last updated: 2017-12-04
3. Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics
Open this publication in new window or tab >>Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics
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2013 (English)In: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, p. 617-626Chapter in book (Refereed)
Abstract [en]

Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

Place, publisher, year, edition, pages
John Wiley & Sons, 2013
Keywords
Alloy thermodynamics, Ti alloys, (Ti-Al)N, (Cr-Al)N
National Category
Condensed Matter Physics Theoretical Chemistry Inorganic Chemistry Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-136443 (URN)10.1002/9781118663547.ch77 (DOI)9781118605813 (ISBN)9781118663547 (ISBN)
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-11-01Bibliographically approved

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