AIMD simulation: increase of the number of the SCF cycles per MD step after some MD steps

Max latevimax.... at
Fri Sep 26 14:13:41 UTC 2014


I've done additional tests to try to figure out what may be going wrong. It 
seems that, 
for the open-shell systems I'm interested in, the performance of the chosen 
is critical. Here's what I understand: the system is in a region of his 
phase space wherein 
after some MD steps, the guess wavefunction obtained by the ASPC method 
starts to 
depart from the BO surface and the use of the computationally cheap 
(full_kinetic, full_single_inverse) do not help speed up the SCF 
convergence. Regularly 
resetting the extrapolation method by restarting the simulation is a 
workaround. But, 
besides being a rather tedious approach, I don't think there is an ideal 
fixed number of 
steps after which to restart the simulation: the issue always tends to show 
up again, later. 

With the full_all preconditioner, the simulation run rather smoothly ! As 
expected, the 
conserved quantity tend to be pretty well conserved over 1.5ps+, when using 
timestep of 0.5fs or even of 1fs. The huge problem now is that a MD step is 
80s in average, with ~80% of the time dedicated to preconditioning. Is 
there a way 
to decrease the time spent in preconditioning ? I'm using currently 
cp2k-2.5.1, the 
mixed_precision algorithm cannot be combined with the full_all 
Is there an other way to do this? Are there changes made to preconditioning 
in the 
development version? 

Best regards,

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