[Pw_forum] About the mean square displacement in CP output

[Bertrand SITAMTZE]

Dear QE users,

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?


Thanks very much for your help


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Bertrand SITAMTZE YOUMBI
Laboratory of Material Sciences
Department of Physics
University of Yaounde I-Cameroon
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