[Pw_forum] C6 unit

[Paolo Giannozzi]

On Sun, 2014-08-17 at 23:27 +0430, Mohamad Moadeli wrote:
> 
> I am doing calculations with QE and I am trying to use DFT-D for a
> combined system, but I do not know what the unit of C6 coefficient is?
> (as implemented)

from the Modules/mm_dispersion.f90 file:

      ! vdw C6 and radii for the first 86 atoms for the DFTD2 method
      ! Data from the DFT-D2 section of the dftd3.f file found on
S.Grimme's home page:
      !
http://www.thch.uni-bonn.de/tc/index.php?section=downloads&subsection=DFT-D3
      ! See also S. Grimme, J. Comp. Chem., 27, 1787 (2006)
      ! First  column: C6, converted to Ry*Bohr^6 units
      ! (in the paper: J*nm^6/mol, conversion factor: 1 J*nm^6/mol =
34.69 Ry*Bohr^6)
      ! Second column: radii, in Bohr (in the paper they are in A)
      !
      DATA vdw_coeffs / &
         4.857,    1.892,&
...

P.

-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222