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Atomistic Computer Simulations of the Melting Process and High Pressure Conditions
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The present work describes the use of atomistic computer simulations in the area of Condensed Matter Physics, and specifically its application to the study of two problems: the dynamics of the melting phase transition and the properties of materials at extreme high pressures and temperatures, problems which defy experimental measurements and purely analytical calculations.

Both classical Molecular Dynamics (using semi–empirical interaction potentials) and first–principles (ab initio) Molecular Dynamics techniques has been applied in this study to the calculation of melting curves in a wide range of pressures for elements such as Xe and H2, the study of the elastic constants of Fe at the conditions of the Earth’s inner core, and the characterization of diffusion and defects formation in a generic Lennard–Jones crystal at the limit of superheating, including the role they play in the triggering of the melting process itself.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , p. 40
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-4826ISBN: 978-91-7415-025-4 (print)OAI: oai:DiVA.org:kth-4826DiVA, id: diva2:14160
Presentation
2008-06-12, Room B22, KTH, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101108Available from: 2008-06-13 Created: 2008-06-13 Last updated: 2010-11-08Bibliographically approved
List of papers
1. Properties of the fcc Lennard-Jones crystal model at the limit of superheating
Open this publication in new window or tab >>Properties of the fcc Lennard-Jones crystal model at the limit of superheating
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2007 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 76, p. 064121-Article in journal (Refereed) Published
Abstract [en]

The face-centered-cubic (fcc) Lennard-Jones (LJ) model can be considered as a representative model of a simple solid. We investigate the mechanism of melting at the limit of superheating in the fcc LJ solid by means of the procedure recently developed by us [Phys. Rev. B 73, 012201 (2006)]. Insight into the mechanism of melting was gained by studying diffusion and defects in the fcc LJ solid by means of molecular dynamics simulations. We found that the limit of superheating achieved by us is likely to be the highest so far. We also found that the size of the cluster which ignites the melting is very small (down to five to six atoms, depending on the size of the supercell) and closely correlates with the linear size of a supercell when the number of atoms varies between 500 and 13 500.

Keyword
STABILITY LIMIT, MOLECULAR-DYNAMICS, CATASTROPHE, LINDEMANN, SURFACE, STATE
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11017 (URN)10.1103/PhysRevB.76.064121 (DOI)000249155200036 ()2-s2.0-34548437497 (Scopus ID)
Note
QC 20100708Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
2. Xenon melting: Density functional theory versus diamond anvil cell experiments
Open this publication in new window or tab >>Xenon melting: Density functional theory versus diamond anvil cell experiments
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2006 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 74, p. 054114-Article in journal (Refereed) Published
Abstract [en]

We performed two-phase ab initio density functional theory based molecular dynamics simulations of Xe melting and demonstrated that, contrary to claims in the recent literature, the pressure dependence of the Xe melting curve is consistent with the corresponding-states theory as well as with the melting curve obtained earlier from classical molecular dynamics with a Xe pair potential. While at low pressure the calculated melting curve is in perfect agreement with reliable experiments, our calculated melting temperatures at higher pressures are inconsistent with those from the most recent diamond anvil cell experiment. We discuss a possible explanation for this inconsistency.

Keyword
MOLECULAR-DYNAMICS, EARTHS CORE, CORRESPONDING STATES, HIGH-PRESSURES, MGO, IRON, KRYPTON, PHASE, TEMPERATURES, SIMULATIONS
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11020 (URN)10.1103/PhysRevB.74.054114 (DOI)000240238400030 ()2-s2.0-33748197844 (Scopus ID)
Note
QC 20100708Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
3. Origin of the Low Rigidity of the Earth's Inner Core
Open this publication in new window or tab >>Origin of the Low Rigidity of the Earth's Inner Core
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2007 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 316, p. 1603-Article in journal (Refereed) Published
Abstract [en]

Earth's solid-iron inner core has a low rigidity that manifests itself in the anomalously low velocities of shear waves as compared to shear wave velocities measured in iron alloys. Normally, when estimating the elastic properties of a polycrystal, one calculates an average over different orientations of a single crystal. This approach does not take into account the grain boundaries and defects that are likely to be abundant at high temperatures relevant for the inner core conditions. By using molecular dynamics simulations, we show that, if defects are considered, the calculated shear modulus and shear wave velocity decrease dramatically as compared to those estimates obtained from the averaged single-crystal values. Thus, the low shear wave velocity in the inner core is explained.

Keyword
NANOCRYSTALLINE METALS, MOLECULAR-DYNAMICS, IRON, ELASTICITY, STRESS, MODEL, GPA
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11021 (URN)10.1126/science.1141374 (DOI)000247239900037 ()2-s2.0-34250837502 (Scopus ID)
Note
QC 20100708Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
4. High-pressure melting curve of hydrogen
Open this publication in new window or tab >>High-pressure melting curve of hydrogen
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2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, p. 194508-Article in journal (Refereed) Published
Abstract [en]

The melting curve of hydrogen was computed for pressures up to 200 GPa, using molecular dynamics. The inter- and intramolecular interactions were described by the reactive force field (ReaxFF) model. The model describes the pressure-volume equation of state solid hydrogen in good agreement with experiment up to pressures over 150 GPa, however the corresponding equation of state for liquid deviates considerably from density functional theory calculations. Due to this, the computed melting curve, although shares most of the known features, yields considerably lower melting temperatures compared to extrapolations of the available diamond anvil cell data. This failure of the ReaxFF model, which can reproduce many physical and chemical properties (including chemical reactions in hydrocarbons) of solid hydrogen, hints at an important change in the mechanism of interaction of hydrogen molecules in the liquid state.

Keyword
density functional theory, equations of state, high-pressure effects, hydrogen, melting, molecular dynamics method
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11022 (URN)10.1063/1.3013704 (DOI)000261141300029 ()2-s2.0-56849103616 (Scopus ID)
Note
QC 20100708Available from: 2009-09-08 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved

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