[CP2K-user] Convergence difference with different number of pocessors for an input

[Mohammad Shakiba]

Hello everyone,

I was using CP2K 6.1.0, compiled with intel 17 and 'psmp' version, for ab 
initio molecular dynamics. My system contains 87 atoms containing Al, O, C 
and H (an MOF). I had two major questions, please help me to find their 
answers.

1- When I use 16 number of processors, it takes 2.5 seconds for each OT 
calculation and when I use 4 processors it takes 2.9 seconds to update OT. 
When I put the number of processors to 20 it takes 270 seconds (about 5 
minutes), put it for 40 it takes 140 seconds and if I put it for 12 
processors it takes more than a minute for each update. My question here is 
just WHY? the following questions are: 
Is there an optimum number of processors? How can I define that? When 
should we use a high number of processors? I have used command 'mpirun -np 
$nprocessors cp2k.psmp -i $input -o $output'.

2- I used 16 number of processors and 4 number of processors. For 'mpirun 
-np 16', it does not converge but for 'mpirun -np 4' it converges slightly 
to the target convergence. I have changed the following commands but the 
convergence for 16 number of processors did not change. Can you explain 
why? What would be the solution to obtain convergence for 16 number of 
processors?

Thanks in advance.

I summarize the commands in the attached input file:

RUN_TYPE MD

!FORCE_EVAL
METHOD Quickstep

!QS
METHOD GPW 

EXTRAPOLATION ASPC 

PERIODIC NONE

PSOLVER  MULTIPOLE 

SCF_GUESS ATOMIC

EPS_SCF 1.0E-6 

PRECONDITIONER FULL_SINGLE_INVERSE ! I also used FULL_ALL

MINIMIZER DIIS ! I also used CG but it converges very slightly and 
sometimes there is no change in the convergence

OPTIMIZER BFGS

ENSEMBLE NVT 

TYPE NOSE


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