On Jul 1, 2006, at 3:24 AM, Mark Abraham wrote:
It seems that you can modify the following line in the function
*mk_nbfp() in force.c and achieve what you want.
C6(nbfp,atnr,i,j) = idef->iparams[k].lj.c6; (it is in line 117
of force.c in version 3.3)
and change it to
C6(nbfp,atnr,i,j) = 0;
This will set the attractive interaction between atom i & j to 0.
More correctly, it will set the coefficient of the r^6 term to zero.
That's the goal.
This
alters the shape of the function for *all* r, both in the "attractive" and
"repulsive" regions,
I could not get that. How could the setting C6(nbfp,atnr,i.j) = 0 can affect the repulsive interaction term, keeping in mind that even if you are using a ff that uses 'sigma' or 'epsilon' to construct C6 and C12 and explicit the minimum of the potential, you are not affecting them?
such that the potential function no longer has a
local minimum.
That's true and that's possibly be the concern of the user who wanted only to switch-off the attractive (c6) vdw without asking for its consequences.
As Erik pointed out, this is very different from having
zero force after a certain r.
Mark
pb.
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