[gmx-users] Combining two Non-bonded potentials

Mehmet Suezen suzen at theochem.tu-muenchen.de
Wed Jan 9 09:52:53 CET 2002

Dear David,

Form of a potential that I was using with another MD program (which I
problems with parallelization) and intent to use this form in Gromacs:

Vij(r) = qi*qj/r + Aij*exp(- Bij*rij)- Cij/rij^6 + 4*eij(
(sij/rij)^18-(sij/rij)^6 )

Simply as I mentioned before it is nothing more than a Buckingham type
potential in
addition with LJ form function. What is the possible solution over 
addition of this type of potential? Should I  hack the source? How easy
to add such form in to source? Your tips are greatly acknowledged.

;[ nonbond_params ] ; if there is a table what should I write in funct
; where I do know a, b and c parameters.
 ai    aj      funct   a       b       c  
  1     1 
  2     2
  1     2

Many Thanks,

David van der Spoel wrote:
> The point is that gromacs right now can work with only one functional
> form, consisting of
> Vij(r) = Aij f(r) + Bij g(r) + qi*qj/(4pi eps0) h(r)
> everything you can do within these bounds is fine. If you need X-X LJ and
> Y-Y Buckingham then it is not possible.
> You have the Aij, Bij and qi/qj in the topology as usual, and the function
> f(r), g(r) and h(r) in the table.xvg file.
> So what kind of function do you want?
> Groeten, David.
> ________________________________________________________________________
> Dr. David van der Spoel,        Biomedical center, Dept. of Biochemistry
> Husargatan 3, Box 576,          75123 Uppsala, Sweden
> phone:  46 18 471 4205          fax: 46 18 511 755
> spoel at xray.bmc.uu.se    spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

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