Editing IDM (section)

= Instructions =

Before start, please read about the Improved Dimer Method by Henkelman & Jónsson [https://aip.scitation.org/doi/10.1063/1.480097] and implemented in VASP by Heyden[http://dx.doi.org/10.1063/1.2104507]. Then kindly follow the procedures detailed here: 

1. Generate your initial guess for the structure (POSCAR). To this end, you can either pre-converge with a NEB calculation, or do it by hand.

2. Be sure the metal or solid phase is frozen and the molecule is relaxed. Do a frequency calculation based on your initial guess. Specify the following in your INCAR file: 

 frequencies:
   IBRION =   5     #     
   EDIFF  =  1E-6   # 
   POTIM  =   0.010 #                  
   NFREE  =   2     # 

3. Based on your POSCAR and OUTCAR of the frequencies calculation, generate in a new folder the input of the IDM with the getdimer script. For example: 

 getdimer ../freq/POSCAR ../freq/OUTCAR POSCAR

4. Specify the following in your INCAR file:

 improved dimer method:
   IBRION =  44     # IDM    
   EDIFF  =   1E-6  # 
   EDIFFG =  -0.030 # use force criteria
   POTIM  =   0.050 # Between 0.010 and 0.100.                  
   NFREE  =   2     # Between 2&5
   FINDIFF=   2     # 
   DIMER_DIST=0.010 #               
   MINROT =   0.010 # 
   STEP_SIZE= 0.010 #                
   STEP_MAX=  0.100 #                
   NSW    = 100     # Never use more than 200. Check periodically for divergence.

5. To check that it is converging well, (1) check with p4vasp that all forces are small, and (2) check that the curvature is always negative. Normal values are between -1.0 and -30.0:
 grep curv OUTCAR