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Extended Lagrangian free energy molecular dynamics
Los Alamos National Lab.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Los Alamos National Lab.
2011 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, nr 16, s. 164111-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Extended free energy Lagrangians are proposed for first principles molecular dynamics simulations at finite electronic temperatures for plane-wave pseudopotential and local orbital density matrix-based calculations. Thanks to the extended Lagrangian description, the electronic degrees of freedom can be integrated by stable geometric schemes that conserve the free energy. For the local orbital representations both the nuclear and electronic forces have simple and numerically efficient expressions that are well suited for reduced complexity calculations. A rapidly converging recursive Fermi operator expansion method that does not require the calculation of eigenvalues and eigen-functions for the construction of the fractionally occupied density matrix is discussed. An efficient expression for the Pulay force that is valid also for density matrices with fractional occupation occurring at finite electronic temperatures is also demonstrated.

Ort, förlag, år, upplaga, sidor
American Institute of Physics (AIP) , 2011. Vol. 135, nr 16, s. 164111-
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:liu:diva-72659DOI: 10.1063/1.3656977ISI: 000296521200012OAI: oai:DiVA.org:liu-72659DiVA, id: diva2:461132
Anmärkning
Funding Agencies|US-DoE|DE-AC52-06NA25396|(U.S.) Department of Energy through the LANL LDRD/ER||Swedish Foundation for Strategic Research (SSF) via Strategic Materials Research Center on Materials Science for Nanoscale Surface Engineering|MS2E|Gran Gustafsson Foundation for Research in Natural Sciences and Medicine||T-Division Ten-Bar Java Group||Tillgänglig från: 2011-12-02 Skapad: 2011-12-02 Senast uppdaterad: 2017-12-08
Ingår i avhandling
1. Development of molecular dynamics methodology for simulations of hard materials
Öppna denna publikation i ny flik eller fönster >>Development of molecular dynamics methodology for simulations of hard materials
2012 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2012. s. 69
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1454
Nationell ämneskategori
Naturvetenskap
Identifikatorer
urn:nbn:se:liu:diva-78823 (URN)978-91-7519-883-5 (ISBN)
Disputation
2012-06-08, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2012-06-21 Skapad: 2012-06-21 Senast uppdaterad: 2012-06-21Bibliografiskt granskad

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