Editing INCAR (section)

==Ionic relaxations==

===DIIS algorithm (IBRION=1)===
The DIIS algorithm converges fast in systems that:
*Are close to an energy minimum (or maximum).
*Have low degrees of freedom.
Examples of those systems are:
*Molecules in vacuum with short backbones (tert-butanol or shorter).
*Bare metal slabs representing closed surfaces. 
*Pre-converged transition states. 

For relaxations use: 
 ionic steps:         
   IBRION =   1     #  
   POTIM  =   0.25  # Between 0.10 and 0.40. 
   EDIFFG =  -0.02  # In eV/Å. 
   NSW    = 100     # Between 50 and 100.      

For '''already pre-converged transition states''' use: 
 ionic steps:         
   IBRION =   1     #  
   POTIM  =   0.01  # Lower than 0.03.                  
   EDIFFG =  -0.05  # In eV/Å
   NSW    =  50     # Between 25 and 50.      

For more information: [http://dx.doi.org/10.1016/0009-2614(80)80396-4] [http://cms.mpi.univie.ac.at/vasp/vasp/IBRION_1_I.html].

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

===CG algorithm (IBRION=2)===

Is the recommended algorithm if you don't know what to do (See Ionic Relaxation Methods in [http://www.vasp.at/index.php?option=com_content&view=article&id=49&Itemid=57]). It is faster and more stable than DIIS for medium and large systems, and always converges into a minimum. 

 ionic steps:         
   IBRION =   2     #  
   POTIM  =   0.150 # Between 0.15 and 0.25.                  
   EDIFFG =  -0.020 # In eV/Å
   NSW    = 100     #  

===Damped MD and QUICKMIN (IBRION=3)===

Recomended to use along NEBs for big systems or in conjunction with NEBs.
 ionic steps:         
   IBRION =   3     #  
   POTIM  =   0.011 # Always lower than 0.020.                   
   EDIFFG =  -0.020 # In eV/Å
   NSW    = 100     #  

POTIM should be very small, lower than the reciprocal of the highest eigenvalue in the Hessian Matrix. For hydrogen-containing systems, this value is around 0.025. Values lower than 0.017 are usually very safe. 
 
Back to [[Núria López and Group]] / [[Scripts_for_VASP]].