# Re: Questions on the definition of parameters

From: jim caldwell <caldwell_at_heimdal.compchem.ucsf.edu>
Date: Tue 29 Aug 2000 12:57:57 -0700 (PDT)

The relationships are found in Fox & Kollman, JPC B. 102, 8070-8079

eps(ij) = sqrt(eps(i)*eps(j))
Rij = Ri + Rj

Aij = eps(ij) * (Rij)**12
Bij = 2 * eps(ij) * (Rij)**6

jim

On Tue, 29 Aug 2000 hsk_at_nemo.physics.ncsu.edu wrote:

> Hi !
>
> I cannot find any clear explanation on how parameters for the van der
> Waals (vdW) interaction of a pair of unlike species are related to those
> read from the parameter file. For example, how do you calculate the
> (6-12) interaction energy between a pair of C and N atoms ? There are
> several issues here.
>
> (1) Is vdW interactiond efined by
>
> V(r) = 4*epsilon*[ (sigma/r)**12 - (sigma/r)**6] ?
>
> Here, 'epsilon' and 'sigma' are potential depth and the characteristic
> distance for the pair interaction.a If this not correct, where can I find
> the correct one ?
>
> (2) Is 'epsilon' defined by the following relation ?
>
> epsilon = (epsilon_1 * epsilon_2)**(1/2),
>
> where 'epsilon_1' and 'epsilon_2' are "well-depth" in the parameter file
> (with the option "KINDNB=RE"). If this is not correct, the where can I
> find the correct relation ?
>
> (3) Is 'sigma' defined by the following relation ?
>
> sigma = (sigma_1 + sigma_2)/2
>
> where 'sigma_1' and 'sigma_2' are so-called vdw radii which are alos from
> the parameter file ?
>
> I tried to find the answers to these questions, and could not.
>
> I hope that I could get answeres soon.
>
> Sincerely,
>
> Hong Seok Kang
>
> Currently, Visiting Profesor to
> Department of Physics
> North Carolina State Universaity
> NC 27607
> (919)515-9123
>
> Aug, 29, 2000
>
>

----------------------------------------------------------------------------
James W. Caldwell (voice) 415-476-8603
Department of Pharmaceutical Chemistry (fax) 415-502-1411
Mail Stop 0446 (email) caldwell_at_heimdal.ucsf.edu
513 Parnassus Avenue
University of California
San Francisco, CA 94143-0446
----------------------------------------------------------------------------
Received on Tue Aug 29 2000 - 12:57:57 PDT
Custom Search