Dear Bertrand: I am not sure I understand how you are extracting the MSD(t) from the CP trajectory: are you just plotting the final values shown in the standard output file, or (as it would be recommended) calculating them by post-processing the trajectory file? In any event, a flat, oscillating MSD(t), after an initial increase, is exactly what you would expect for a solid.
Antonio Tilocca UCL >From siyouber at yahoo.fr Thu Apr 29 15:09:27 2010 >From: siyouber at yahoo.fr (Bertrand SITAMTZE) >Date: Thu, 29 Apr 2010 13:09:27 +0000 (GMT) >Subject: [Pw_forum] About the mean square displacement in CP output >I am running CP dynamic with fixed temperature for a given solid system, >using cp.x. The microcanonical calculation went very well with a >conserved energy.Now the energy is still conserved. But my emphasis is on > the mean >square displacement(MSD) of atoms. They are calculated and plotted as a >function of time. At the begining, the dependence seems to be linear at >after, the MSD seem to oscillate around certain values which can be taken >as a mean value after a sufficiently long time. My questions are: 1) >According to the litterature, the dependence at the beginning should be >quadratic and became linear after a long time. But for condensed system >as >a solid it is, the MSD should saturate after a very long time. What is >happening for my case? 2) The MSD computed with cp.x are tree >dimensionnal. Please, confirm it or not. 3) In which file should I see >how >those MSD are computed?
