Re: CCL:diffusion coefficient from mean square displacement



Hannes Loeffler wrote:
 I assume you are using periodic boundary conditions
 for the bulk liquid. Make sure you are treating
 periodic boundary conditions correctly in the calculation
 of the MSD.
 Richard Gillilan
 MacCHESS Cornell
 >
 > Hello,
 >
 > I'm currently trying to obtain the diffusion coefficient from the mean
 square
 > displacement (as a test case I simulated pure water). The diffusion
 coefficient
 > may than be derived from the long time behavior of the MSD curve (slope).
 >
 > But what does "long time" mean? I observe that the MSD curve
 becomes nearly
 > linear after a few pico second but after some pico seconds later the line
 starts
 > to rise again with an obviously larger slope.  Does this tell me anything
 about
 > the quality of the potential used?  Should I be concerned about the
 "non-linear"
 > MSD curve?
 >
 > Hannes.
 >
 > --
 > Hannes Loeffler | tel: +43-(0)512-507-5166 | fax: +43-(0)512-507-2714
 > http://www-c724.uibk.ac.at/staff/loeffler/ | mailto:Hannes.Loeffler-0at0-uibk.ac.at
 > Institute for General, Inorganic and Theoretical Chemistry
 > University of Innsbruck, Austria
 >
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