Editing INCAR (section)

==Parallelization==

Tune '''NPAR''' (or '''NCORE''', never both), '''NSIM''', '''KPAR''', and  '''NBANDS''' to parallelive well. 
Changing the parameter '''NPAR''' could increase the speed of calculation without affecting the global energy. Please see [http://cms.mpi.univie.ac.at/vasp/guide/node138.html] and made some test before set large systems. 
NPAR must be exactly equal to (1) the number of cores per node if you are using one node, or (2) the number of nodes if you are using more than one node. NEVER USE THE SQUARE ROOT RULE PROPOSED IN THE VASP MANUAL, it is two-decades outdated!  

Optimal '''NPAR''' values:

  Nº Queue
   4 c4m8         ==> NPAR =  4
   8 c4m8         ==> NPAR =  2
  12 c4m8         ==> NPAR =  3
 etc.
    
   8 c8m24        ==> NPAR =  8
  16 c8m24        ==> NPAR =  2
  24 c8m24        ==> NPAR =  3
 etc.
 
  12 c12m48ib     ==> NPAR = 12
  24 c12m48ib     ==> NPAR =  2
  36 c12m48ib     ==> NPAR =  3
  48 c12m48ib     ==> NPAR =  4
 etc.
 
  48 MareNostrum4 ==> NPAR = 48
  96 MareNostrum4 ==> NPAR =  2
 144 MareNostrum4 ==> NPAR =  3
 192 MareNostrum4 ==> NPAR =  4
 etc.
 
  16 MareNostrum3 ==> NPAR = 16
  32 MareNostrum3 ==> NPAR =  2
  48 MareNostrum3 ==> NPAR =  3
  64 MareNostrum3 ==> NPAR =  4
 etc. 

A calculation running on 8 processors-c8m24 will finish around 30% faster than on 8 processors-c4m8.

'''NSIM''' can be set if your INCAR file states the following:

 IALGO=48   or   ALGO=Fast   or   ALGO=VeryFast

You can speed up your calculation by ~15% varying the NSIM parameter. There should be no difference in the total energy and the convergence behavior in setting NSIM>1, only the performance should improve. The default value is 4. 

  In c4m8        ==> NSIM = between 6 and 16
  In c8m24       ==> NSIM = between 8 and 16
  In c12m48ib    ==> NSIM = between 8 and 16
  In MareNostrum ==> NSIM = between 10 and 42

Recomended values: 
 NSIM =  8   for c4m8 & c8m24
 NSIM = 12   for c12m48ib
 NSIM = 32   for MareNostrum

For more information [http://cms.mpi.univie.ac.at/vasp/guide/node130.html]

You can further increase the efficiency of your parallelization by setting '''KPAR''' and '''NBANDS'''. You must know the kind of processors you are working with, the number of electrons/bands in your calculation, and to read the VASP manual. 

It is a must to use advanced parallelization when working in MareNostrum and for big projects where lots of computational hours are spent. 

Back to [[Núria López and Group]] / [[Scripts_for_VASP]].