Editing INCAR (section)

=Additional parameters=

==Verbosity==

'''Tip''': Add this segment in your INCAR file to reduce verbosity and avoid writing WAVECAR and CHG(CAR) files: 
 # Verbosity:  
   NWRITE =   0     # Verbosity 
   LWAVE  =   F     # WAVECAR      
   LCHARG =   F     # CHG / CHGCAR

Other flags that affect the files being written: 
   '''FLAG     DEFAULT # FILE'''
   NWRITE =   2     # Verbosity of the OUTCAR file 
   LWAVE  =   T     # WAVECAR       [http://cms.mpi.univie.ac.at/vasp/guide/node64.html]
   LCHARG =   T     # CHG / CHGCAR  [http://cms.mpi.univie.ac.at/vasp/guide/node63.html] [http://cms.mpi.univie.ac.at/vasp/vasp/CHGCAR_file.html]
   LVTOT  =   F     # LOCPOT        [http://cms.mpi.univie.ac.at/vasp/vasp/LOCPOT_file.html]  
   LELF   =   F     # ELFCAR        [http://cms.mpi.univie.ac.at/vasp/guide/node72.html]  
   PARCHG =   F     # PARCHG         
   LAECHG =   F     # Bader AECCAR files  
   LORBIT =   0     # PDOS/LDOS       

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

==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 NEVER USE THE SQUARE ROOT RULE PROPOSED IN THE VASP MANUAL, it is two-decades outdated!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]].

==Tips for efficient electronic relaxations==

*Some simple systems, such as molecules and conductors, allow you to use the Fast algorithm. This algorithm parallelizes well. 
   ALGO   =   Fast  # Normal: general purpouse; Fast: Good for conductors. 

*For relaxations in big systems and NEBs, lowering the threshold for electronic convergence can save a lot of cpu-hours. Increase NELMIN to preserve accuracy after several ionic steps:
   EDIFF  =   1E-3  # Or 1E-4 for each moving nucleus in your POSCAR file
   NELMIN =   5     # Or 5. To increase this value further may rise computational burden without adding precision to the forces.  

*For very precise calculations, a rule-of-thumb is EDIFF=EDDIFG*0.1 if EDDIFG is positive (energy criterion), or EDIFF=-EDDIFG*0.001 if EDIFFG is negative (force criterion).


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

==Improving stability: Mixing parameters==
If you have problems to reach convergence in the first electronic loop, and you are not reading WAVECAR, set:
 NELMDL = -9   # Number of non self-consistent electronic steps at the beginning (w/o CHG update)

Otherwise, vary these mixing scheme parameters (you can play with them):
 AMIX   = 0.10            
 BMIX   = 0.01           
 AMIN   = 0.10          

If problems persist, increase BMIX and reduce AMIN: 
 AMIX   = 0.10            
 BMIX   = 3.00            
 AMIN   = 0.01             

If problems persist, read this [[http://www.vasp.at/vasp-workshop/slides/optelectron.pdf]]

References: [http://cms.mpi.univie.ac.at/vasp/guide/node131.html] and  [http://cms.mpi.univie.ac.at/vasp/vasp/Mixing_tags_IMIX_INIMIX_MAXMIX_AMIX_BMIX_AMIX_MAG_BMIX_MAG_AMIN_MIXPRE_WC.html]

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