7.15 What combinations are useful, for initialization

 

Here are a few useful settings for the initialization and electronic minimization

• For static calculations, just remove the WAVECAR file and start from scratch, no parameters must be specified. The defaults will be:

  ISTART 0 startjob: no WAVECAR file

  ICHARG 2 charge: from atoms

  INIWAV 1 random initialization for wf.

  NELM 40 maximum of 40 electronic steps

  NELMIN 2 minimum of two steps

  NELMDL -3 no update of charge for 3 steps

  EDIFF accuracy for electronic minimization

• In several cases it makes sense to start from an old WAVECAR file (for instance to continue relaxation or to continue with increased ENCUT). In this case just keep the WAVECAR file and start vasp, the defaults will be now:

  ISTART 1 continue from WAVECAR file

  ICHARG 0 charge from wavefunctions

  NELM 40 maximum of 40 electronic steps

  NELMIN 2 minimum of two steps

  NELMDL 0 immediately update charge

  You should set ICHARG=1 by hand if the old CHGCAR file also exists, if there is strong charge sloshing this will save a few steps, in comparison with the default setting.
• Efficient relaxation, from a starting guess far away from reasonable:

  It can make sense to overwrite several of the default parameters if you want to do an efficient relaxation from a starting configuration, which is not close to the minimum, set the following values in the INCAR file:

  NELMIN = 4    !  do a minimum of four steps
  EDIFF  = 1E-2 !  low accuracy
  EDIFFG = 1E-4 !  accuracy of ions must be much better
  NSW    = 20   !  20 ionic steps in ions
  IBRION =  2   !  use CG algorithm for ions

  This way the only low accuracy will be required, in the first few steps, but always a minimum of 4 electronic steps is done. Therefore the accuracy will improve during the optimization of the ionic positions.