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Computer simulation of materialsunder extreme conditions
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.ORCID iD: 0000-0002-5307-5757
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Extreme conditions allow us to reveal unusual material properties. At the same time an experimental approach is di-cult under such conditions. Capabilities of a theoretical approach based on simplied models are limited. This explainsa wide application of computer simulations at extreme conditions. My thesis is concerned with computer simulations undersuch a conditions. I address such problems as melting, solidsolid phase transitions, shockwave impact on material properties and chemical reactions under extreme conditions. We addressed these problems to facilitate simulations of phase transitions to provide some interpretation of experimental data andexplain enigmatic phenomena in interior of the Earth.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , ix, 83 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2016:27
Keyword [en]
ab initio, molecular dynamics, phase transition, metadynamics
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-188146ISBN: 9789177290353 (print)OAI: oai:DiVA.org:kth-188146DiVA: diva2:933622
Public defence
2016-06-15, FB52, Albanova Universitetscentrum, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160615

Available from: 2016-06-15 Created: 2016-06-07 Last updated: 2016-06-15Bibliographically approved
List of papers
1. Melting of a polycrystalline material
Open this publication in new window or tab >>Melting of a polycrystalline material
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2013 (English)In: The European Physical Journal Special Topics, ISSN 1951-6355, E-ISSN 1951-6401, Vol. 216, no 1, 199-204 p.Article in journal (Refereed) Published
Abstract [en]

Calculating the melting temperature of a solid with a known model of interaction between atoms is nowadays a comparatively simple task. However, when one simulates a single crystal by molecular dynamics method, it does not normally melt at the melting temperature. Instead, one has to significantly overheat it. Yet, a real material melts at the melting point. Here we investigate the impact of the defects and the grain boundaries on melting. We demonstrate that defects and grain boundaries have similar impact and make it possible to simulate melting in close vicinity of thermodynamic melting temperature. We also show that the Z method might be non-applicable in discriminating a stable submelting phase.

Keyword
Argon
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-119060 (URN)10.1140/epjst/e2013-01743-1 (DOI)000314364300021 ()2-s2.0-84873507587 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130306

Available from: 2013-03-06 Created: 2013-03-05 Last updated: 2017-12-06Bibliographically approved
2. Impact of crystal lattice defects on crystal melting: A molecular dynamics study
Open this publication in new window or tab >>Impact of crystal lattice defects on crystal melting: A molecular dynamics study
2013 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 79, 95-98 p.Article in journal (Refereed) Published
Abstract [en]

An ideal infinite lattice, when subjected to heating does not melt at the thermodynamic melting temperature. Instead, it remains solid metastably up to considerably higher temperatures. This effect is called superheating. We performed a molecular dynamics simulation of Xenon using Lennard-Jonesium potential with several types of defects. We observed a superheating effect on the chosen model for several pressures and found that the presence of grain inclusion or grain interface eliminates the superheating effect.

Keyword
Superheating, Overheating, Lennard-Jonesium, Melting
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-132197 (URN)10.1016/j.commatsci.2013.06.026 (DOI)000324471100014 ()2-s2.0-84879937895 (Scopus ID)
Note

QC 20131024

Available from: 2013-10-24 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
3. A metadynamics study of the fcc-bcc phase transition in Xenon at high pressure and temperature
Open this publication in new window or tab >>A metadynamics study of the fcc-bcc phase transition in Xenon at high pressure and temperature
2015 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 107, 66-71 p., 6523Article in journal (Refereed) Published
Abstract [en]

Abstract To theoretically find a stable solid phase is not a trivial task even at 0 K. The difficulties multiply at high temperature (T) because even more elaborate crystal structure prediction methods fail in the vicinity of the melting transition. Moreover, if the submelting phase is dynamically unstable at low T some methods cannot be applied at all. The method of metadynamics allows finding local minima of Gibbs free energy without additional simplifications. However, so far this method has been mainly used for study of pressure-induced solid-solid phase transitions and not in searching for T-induced ones. Here we study the applicability of the technique to the latter class of problems as well as to the approximate determination of the transition temperature. We apply the metadynamics method to study the solid-solid phase transition in Xe described by the Buckingham potential at high temperature and observe the fcc-bcc phase transition in a pressure-temperature range consistent with earlier results.

Keyword
Buckingham potential, Dynamical stability, Metadynamics, Solid-solid phase transition
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-170224 (URN)10.1016/j.commatsci.2015.04.055 (DOI)2-s2.0-84930945679 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20150630

Available from: 2015-06-30 Created: 2015-06-29 Last updated: 2017-12-04Bibliographically approved
4. Sound velocity in shock compressed molybdenum obtained by ab initio molecular dynamics
Open this publication in new window or tab >>Sound velocity in shock compressed molybdenum obtained by ab initio molecular dynamics
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 6, 060101Article in journal (Refereed) Published
Abstract [en]

The sound velocity of Mo along the Hugoniot adiabat is calculated from first principles using density-functional theory based molecular dynamics. These data are compared to the sound velocity as measured in recent experiments. The theoretical and experimental Hugoniot and sound velocities are in very good agreement up to pressures of 210 GPa and temperatures of 3700 K on the Hugoniot. However, above that point the experiment and theory diverge. This implies that Mo undergoes a phase transition at about the same point. Considering that the melting point of Mo is likely much higher at that pressure, the related change in the sound velocity in experiment can be ascribed to a solid-solid transition.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-175935 (URN)10.1103/PhysRevB.92.060101 (DOI)000362212200001 ()2-s2.0-84941102577 (Scopus ID)
Funder
Swedish Research Council, 2013-5767Swedish Research Council, 2014-4750
Note

QC 20151103

Available from: 2015-11-03 Created: 2015-10-26 Last updated: 2017-12-01Bibliographically approved
5. Synthesis of heavy hydrocarbons at the core-mantle boundary
Open this publication in new window or tab >>Synthesis of heavy hydrocarbons at the core-mantle boundary
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2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, 18382Article in journal (Refereed) Published
Abstract [en]

The synthesis of complex organic molecules with C-C bonds is possible under conditions of reduced activity of oxygen. We have found performing ab initio molecular dynamics simulations of the C-O-H- Fe system that such conditions exist at the core-mantle boundary (CMB). H2O and CO2 delivered to the CMB by subducting slabs provide a source for hydrogen and carbon. The mixture of H2O and CO2 subjected to high pressure (130 GPa) and temperature (4000 to 4500 K) does not lead to synthesis of complex hydrocarbons. However, when Fe is added to the system, C-C bonds emerge. It means that oil might be a more abundant mineral than previously thought.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Mineral and Mine Engineering
Identifiers
urn:nbn:se:kth:diva-180487 (URN)10.1038/srep18382 (DOI)000366571400001 ()26675747 (PubMedID)2-s2.0-84950349897 (Scopus ID)
Note

QC 20160115

Available from: 2016-01-15 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved

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