some strange phenomena on running CP2K with PBE functional

[huan... at mail.huji.ac.il]

Dear All,

I am a newbie on CP2K and I have some questions on running CP2K with PBE 
functional.

Last week I did some tests on my benzene-water cluster project using both 
BLYP and PBE functional. I found that for BLYP functional, 8 CPU was the 
best choice for my research system, while using more CPUs for MD 
simulation, such as 16, 24, 32, the speed for every step slowed down. It 
can be explained that the more CPUs I used, the more time spent on 
communication.

But when it comes to PBE functional, no matter how many CPUs I used, the 
calculation speed always slowed down after about 40 steps. (The first 40 
steps, the calculation just take about 50 seconds per step, but after 44 
steps, it takes about 300 second for each step). Please see my *
nve_PBE_50steps.ener* file in attachment. Actually, the structure of the 
benzene-water cluster is the same for both BLYP and PBE input files. And I 
just changed the functional into PBE, choosing the potential as GTH-PBE 
type, and using the same basis set as BLYP functional used. The rest of 
setting are the same with the input file of BLYP functional. I also 
attached the output file for detail information. (*nve_PBE_50steps.out*)

These decreasing of speed phenomena also happened when I used more than 8 
CPU with BLYP functional. But if I use 8 CPU for calculation with BLYP 
functional, the speed was very stable, which was about 40 seconds per step.

My question is why the calculation speed slow down after 40 steps when I 
use PBE functional? Why the speed could not stable as using BLYP functioanl?

Best regards,
Huan

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