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Extended Lagrangian Born-Oppenheimer molecular dynamics with dissipation
Los Alamos National Laboratory.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
Los Alamos National Laboratory.
Los Alamos National Laboratory.
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2009 (English)In: JOURNAL OF CHEMICAL PHYSICS, ISSN 0021-9606, Vol. 130, no 21, 148075- p.Article in journal (Refereed) Published
Abstract [en]

Stability and dissipation in the propagation of the electronic degrees of freedom in time-reversible extended Lagrangian Born-Oppenheimer molecular dynamics [Niklasson , Phys. Rev. Lett. 97, 123001 (2006); Phys. Rev. Lett. 100, 123004 (2008)] are analyzed. Because of the time-reversible propagation the dynamics of the extended electronic degrees of freedom is lossless with no dissipation of numerical errors. For long simulation times under "noisy" conditions, numerical errors may therefore accumulate to large fluctuations. We solve this problem by including a dissipative external electronic force that removes noise while keeping the energy stable. The approach corresponds to a Langevin-like dynamics for the electronic degrees of freedom with internal numerical error fluctuations and external, approximately energy conserving, dissipative forces. By tuning the dissipation to balance the numerical fluctuations the external perturbation can be kept to a minimum.

Place, publisher, year, edition, pages
2009. Vol. 130, no 21, 148075- p.
Keyword [en]
ab initio calculations, fluctuations, molecular dynamics method
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-19532DOI: 10.1063/1.3148075OAI: oai:DiVA.org:liu-19532DiVA: diva2:225757
Available from: 2009-06-29 Created: 2009-06-26 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.
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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Steneteg, Peter

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