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Equation of state of paramagnetic CrN from ab initio molecular dynamics
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 14, 144404- p.Article in journal (Refereed) Published
Abstract [en]

The equation of state for chromium nitride has been debated in the literature in connection with a proposed collapse of its bulk modulus following the pressure-induced transition from the paramagnetic cubic phase to the antiferromagnetic orthorhombic phase [F. Rivadulla et al., Nature Mater. 8, 947 (2009); B. Alling et al., ibid. 9, 283 (2010)]. Experimentally the measurements are complicated due to the low transition pressure, while theoretically the simulation of magnetic disorder represents a major challenge. Here a first-principles method is suggested for the calculation of thermodynamic properties of magnetic materials in their high-temperature paramagnetic phase. It is based on ab initio molecular dynamics and simultaneous redistributions of the disordered but finite local magnetic moments. We apply this disordered local moments molecular dynamics method to the case of CrN and simulate its equation of state. In particular the debated bulk modulus is calculated in the paramagnetic cubic phase and is shown to be very similar to that of the antiferromagnetic orthorhombic CrN phase for all considered temperatures.

Place, publisher, year, edition, pages
American Physical Society , 2012. Vol. 85, no 14, 144404- p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-76936DOI: 10.1103/PhysRevB.85.144404ISI: 000302401900004OAI: oai:DiVA.org:liu-76936DiVA: diva2:524589
Note
Funding Agencies|Swedish Research Council (VR)|621-2011-4426621-2011-4417|Swedish Foundation for Strategic Research (SSF)|10-0026|Available from: 2012-05-03 Created: 2012-04-27 Last updated: 2017-12-07
In thesis
1. Development of molecular dynamics methodology for simulations of hard materials
Open this publication in new window or tab >>Development of molecular dynamics methodology for simulations of hard materials
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on molecular dynamics simulations, both classical and ab initio. It is devoted to development of new methods and applications of molecular dynamics based techniques to a series of materials, all of which have the common property of being hard.

I first study grain boundaries in diamond and apply a novel method to better explore the configurational phase space. Using this method several new grain boundary structures are found. The lowest energy grain boundary structure has 20% lower energy then the one obtained with a conventional approach.

Another area is the development of efficient methods for first principles Born-Oppenheimer molecular dynamics. Here a fundamental shortcoming of the method that limits efficiency and introduces drift in the total energy of the system, is addressed and a solution to the problem is presented. Special attention is directed towards methods based on plane waves. The new molecular dynamics simulation method is shown to be more efficient and conserves the total energy orders of magnitude better then previous methods.

The calculation of properties for paramagnetic materials at elevated temperature is a complex task. Here a new method is presented that combines the disordered local moments model and ab initio molecular dynamics. The method is applied to calculate the equation of state for CrN were the connection between magnetic state and atomic structure is very strong. The bulk modulus is found to be very similar for the paramagnetic cubic and the antiferromagnetic orthorhombic phase.

TiN has many applications as a hard material. The effects of temperature on the elastic constants of TiN are studied using ab initio molecular dynamics. A significant dependence on temperature is seen for all elastic constants, which decrease linearly with temperature.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 69 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1454
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-78823 (URN)978-91-7519-883-5 (ISBN)
Public defence
2012-06-08, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2012-06-21Bibliographically approved

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