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

[Max]

Dear CP2K users and developers, 

I would like to perform a MD simulation for a transition metal complex in 
water; 
the complex being in an open-shell state. However, I'm facing an issue 
which I 
cannot resolve: the time taken by a MD step dramatically increases after 
some 
steps because of the increase of the number of SCF cycles (see 
Figure_1.eps). 


I first thought that this was due to the order chosen for the wavefunction 
extrapolation 
(ASPC 3), but the situation does not change when varying the order (1-4). 

I usually tend to use rather conservative values for EPS_DEFAULT and CUTOFF 
(1e-14 and 1000 Ry), and I was wondering if this could lead to a numerical 
instability 
in the present case. However increasing EPS_DEFAULT to 1e-12 does not 
improve 
the situation; likewise for using a smaller CUTOFF value of 500 Ry. 

Please note that, when the simulation is restarted, the same phenomenon in 
observed. 
Thus, in Figure_2.eps, the simulation was restarted at ~1070 fs. 

I made several attempts to find which mistake(s) I could have made (CG vs 
DIIS 
minimizer; EPS_SCF value of 1e-6 or 5e-7; CSVR versus NHC thermostating; 
TIMESTEP 
of 0.25 or 0.50 fs; PRECONDITIONER and ENERGY_GAP ...): but nothing came 
out of 
this. 

There is perhaps a trivial error which I may be missing. Please let me 
know: I have 
attached the input file to the message. 


Thanks in advance for your help. 

Best regards,
Max


P.S. For Figure_1.eps, the simulation was perfomed using the attached input 
file. For 
Figure_2.eps, there are the following changes: "EPS_DEFAULT 1.0E-12", 
"EXTRAPOLATION_ORDER 1", "PRECONDITIONER FULL_SINGLE_INVERSE". 


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