[CP2K-user] Convergence difference with different number of pocessors for an input
Mohammad Shakiba
mshakiba.k... at gmail.com
Fri Mar 8 18:43:25 UTC 2019
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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