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Missing-atom structure of diamond Sigma 5 (001) twist grain boundary
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
University of Bayreuth.
University of Bayreuth.
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2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 14, 144112- p.Article in journal (Refereed) Published
Abstract [en]

We carried out a combined experimental and theoretical study of grain boundaries in polycrystalline diamond, aimed at achieving the conditions in which grain boundaries are equilibrated. Raman spectra of compacted at high-pressure and high-temperature diamond powders allow us to identify signals from sp(2)-bonded atoms, in addition to a strong peak at 1332 cm(-1), corresponding to sp(3)-bonded carbon. To verify our interpretation of the experiment, Sigma 5 (001) twist grain boundaries of polycrystalline diamond were studied by means of molecular dynamics simulations using the technique proposed by von Alfthan et al. [Phys. Rev. Lett. 96, 055505 (2006)]. We find that grain-boundary (GB) configurations, from which one atom is removed, have significantly lower energy compared to those obtained with conventional techniques. These calculated GBs are highly ordered, a few monolayers thick, in agreement with experimental observations, and are primarily sp(2) bonded. This paper underlines the importance of varying the number of atoms within GBs in molecular dynamics simulations to correctly predict the GB ground-state structure.

Place, publisher, year, edition, pages
American Physical Society , 2011. Vol. 84, no 14, 144112- p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-72025DOI: 10.1103/PhysRevB.84.144112ISI: 000296287600002OAI: diva2:456009
Funding Agencies|Swedish Foundation for Strategic Research via strategic center MS2E||Goran Gustafsson Foundation for Research in Natural Sciences and Medicine||Swedish Research Council (VR)||DFG|SPP1236|Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2012-06-21
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.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1454
National Category
Natural Sciences
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)
Available from: 2012-06-21 Created: 2012-06-21 Last updated: 2012-06-21Bibliographically approved

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