units in GENPOT section

Noam Bernstein no... at bollweevil.gdbg.org
Wed Jun 2 15:23:39 UTC 2010

Hi all - I'm trying to set up a DFT calculation with vdW corrections,
in the form of a non-bonded potential.  I've been looking at the
example in tests/QS/regtest-dft-vdw-corr, where I found the
following section.

         ATOMS        C  C
         RCUT [angstrom]        14.9
         RMIN [angstrom]        0.2
         RMAX [angstrom]        15.0
         VARIABLES    R
         PARAMETERS   CSIX      RZERO    D
         VALUES      -216.9850 6.57936 2.9688
         FUNCTION    (CSIX/(R**6))*((1.0 - EXP(-1.0*D*((R/RZERO)**7)))**4)

I think I understand what it's doing, and the functional form is consistent
with what's in, for example, Williams and Malhotra (Chem Phys v 327).
However, I haven't been able to figure out what are the units.  The
PARAMETERS must implicit have units (CSIX must be in units of
energy*length^6, e.g.), but the documentation says that PARAMETERS are
in cp2k_internal units, and I couldn't find those defined on the units page of
the documentation.  Is my guess that  they're Hartree and Bohr correct?


P.S. Is there another good source of parameters that I should know about,
in addition to that Williams and Malhotra paper?

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