Studies of surface diffusion and dissipative particel dynamics

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en Nikunen, Petri 2012-02-17T07:35:51Z 2012-02-17T07:35:51Z 2006-03-18
dc.identifier.isbn 951-22-8059-0
dc.identifier.issn 1457-1404
dc.description.abstract In the first part of this thesis, we study diffusion of atoms on solid surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W(110), first on clean surfaces and then on surfaces containing small concentrations of quenched (immobile) impurities. In both cases, we examine how thermodynamic non-equilibrium affects tracer diffusion and collective diffusion of atoms on a surface. We find that non-equilibrium effects can play an important role when there are strong interactions in the system. These effects persist even when there are only slight deviations from equilibrium. We also find that even minute impurity concentrations can lead to major changes in the diffusion coefficients. The combined effect is not, however, additive. Indeed, we find that the non-equilibrium effects are most pronounced on clean surfaces, while on surfaces covered by impurities the role of non-equilibrium conditions is weaker. This is essentially due to the similarity between disorder as induced either by the non-equilibrium condition or by the presence of impurities on the surface. In the second part of the thesis, we consider methodological aspects of the dissipative particle dynamics (DPD) technique. First, we address the question: "How to integrate the equations of motion in DPD simulations?" We test and analyze several novel DPD integration schemes on an equal footing through DPD simulations of different model systems. By monitoring a number of physical observables including temperature, radial distribution function, radius of gyration for polymers, and tracer diffusion, we find that the methods by Lowe and Shardlow give the best overall performance and are superior also to the integrators tested in previous studies. Second, we study the dynamics of polymer melts. In standard DPD, as well as in other coarse-grained soft potential models, there is a problem that polymers can penetrate through themselves. This is a clear artifact, and has direct consequences on polymer dynamics. To correct this problem, we tune the conservative forces within the polymer chain so strong that chains cannot cut through each other. Indeed, if a certain geometric criterion is met, it is impossible for polymer chains to cross. Through DPD simulations, we show that our approach is able to reproduce the Rouse-like dynamics for short chains and reptational dynamics for longer chains. The results are in good agreement with polymer theories and experiments. en
dc.format.extent 95, [47]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries Helsinki University of Technology Laboratory of Computational Engineering publications. Report B en
dc.relation.ispartofseries 53 en
dc.relation.haspart P. Nikunen, I. Vattulainen, and T. Ala-Nissila, Non-equilibrium effects in profile evolution measurements of surface diffusion, Surface Science 447, L162 (2000). [article1.pdf] © 2000 Elsevier Science. By permission.
dc.relation.haspart P. Nikunen, I. Vattulainen, and T. Ala-Nissila, Density profile evolution and nonequilibrium effects in partial and full spreading measurements of surface diffusion, Journal of Chemical Physics 114, 6335 (2001). [article2.pdf] © 2001 American Institute of Physics. By permission.
dc.relation.haspart P. Nikunen, I. Vattulainen, and T. Ala-Nissila, Effects of quenched impurities on surface diffusion, spreading, and ordering of O/W(110), Journal of Chemical Physics 117, 6757 (2002). [article3.pdf] © 2002 American Institute of Physics. By permission.
dc.relation.haspart P. Nikunen, M. Karttunen, and I. Vattulainen, How would you integrate the equations of motion in dissipative particle dynamics simulations?, Computer Physics Communications 153, 407 (2003). [article4.pdf] © 2003 Elsevier Science. By permission.
dc.relation.haspart P. Nikunen, I. Vattulainen, and M. Karttunen, Reptational dynamics in dissipative particle dynamics simulations of polymer melts, Physical Review E, submitted for publication (December, 2005); Helsinki Institute of Physics preprint HIP–2005–54/Th. [article5.pdf] © 2005 by authors.
dc.subject.other Electrical engineering en
dc.subject.other Physics en
dc.title Studies of surface diffusion and dissipative particel dynamics en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Electrical and Communications Engineering en
dc.contributor.department Sähkö- ja tietoliikennetekniikan osasto fi
dc.subject.keyword computer simulation en
dc.subject.keyword integration scheme en
dc.subject.keyword non-equilibrium en
dc.subject.keyword soft matter en
dc.identifier.urn urn:nbn:fi:tkk-006685
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Computational Engineering en
dc.contributor.lab Laskennallisen tekniikan laboratorio fi

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