[Pw_forum] Problem with postprocessing of the vc-cp

[Nekrashevich Sergey]

Dear all,
I've found a bit strange behavior of cppp.x tool while dealing with 
vc-cp dynamics of 167-atomic supercell of silicon nitride.
I perfomed the 500 steps of variable-cell Car-Parrinello molecular 
dynamics and then ran it through cppp.x to have an AXSF-file as output. 
After opening the animation in the XCRYSDEN I can see, that during some 
number of steps atoms are moving properly from their initial positions 
(which were achieved after ionic relaxation). But then at some certain 
time step atoms revert to their original positions specified in the 
input file for cp.x. After that atoms are starting to move continuously 
again, but after some steps the leap is reapeted. It's obvious that such 
movement does not correspond to real behavior of the system, at least 
because in the cp.x output file there are no leaps in atomic positions 
(I've checked it by putting 'iprint = 1').
Any help is greatly appreciated.

Best regards,
Nekrashevich Sergey.