[QE-users] PBE + vdW or Grimme-D3

[Giuseppe Mattioli]

Dear Sohail
They are two main ways to simulate dispersion forces in QE. You may  
look into the corresponding documentation, printed in the pw.x output  
if you use one of them. VDWDF is actually a family of functionals in  
which dispersion forces are calculated as a functional of the density.  
They are not limited to pbe+vdw and there are several flavors  
(c09-vdwdf, vdwdf2, also a hybrid c09-vdwdf-x functional, among  
others). DFT-D2, D3, also D4 (not implemented in QE) are developed by  
Stefan Grimme's group. They are rather a semiempirical contribution  
added to the ab initio calculation in which correlation functionals  
neglect long-range dispersion contributions. Let us add also rVV10,  
XDM and TS to the families. rVV10 and TS are more or less similar to  
the first two. XDM is pretty different. As *all of them* simulate the  
same thing, all can in principle satisfy your needs. Hence you may 1)  
use the setup someone else you trust used in publications or 2) make  
yourself some tests by using layered unit cells to see what is the  
best setup for your system.
HTH
Giuseppe

Quoting Sohail Ahmad <sohailphysics at yahoo.co.in>:

> Dear QE experts 
> 1.   May I know the difference between PBE+vdW  and  Grimme-D32.    
> Which one is more suitable to study the effect of vdW in case of  
> Transition metal dichalcogenide bi/tri/quad layer and why ?
> Best Wishes
> Sohail KKU, Abha, Saudi Arabia



GIUSEPPE MATTIOLI
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