[gmx-users] Van der Waals: switch attractive term off

[Mark Abraham]

> 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. This
alters the shape of the function for *all* r, both in the "attractive" and
"repulsive" regions, such that the potential function no longer has a
local minimum. As Erik pointed out, this is very different from having
zero force after a certain r.

Mark