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Electronic and atomic structure of Mo from high-temperature molecular dynamics simulations
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Applied Materials Physics, Department of Material Science and Engineering, The Royal Institute of Technology, 10044 Stockholm, Swedent.
Linköpings universitet, Institutionen för datavetenskap, Statistik. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
(engelsk)Manuskript (preprint) (Annet (populærvitenskap, debatt, mm))
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.

Identifikatorer
URN: urn:nbn:se:liu:diva-53779OAI: oai:DiVA.org:liu-53779DiVA, id: diva2:291828
Tilgjengelig fra: 2010-02-03 Laget: 2010-02-03 Sist oppdatert: 2010-02-11
Inngår i avhandling
1. Effects of disorder in metallic systems from First-Principles calculations
Åpne denne publikasjonen i ny fane eller vindu >>Effects of disorder in metallic systems from First-Principles calculations
2010 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Linköping: Linköping University Electronic Press, 2010. s. 126
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1299
Emneord
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
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-53584 (URN)978-91-7393-445-9 (ISBN)
Disputas
2010-03-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2010-02-11 Laget: 2010-01-25 Sist oppdatert: 2010-03-29bibliografisk kontrollert

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