[gmx-users] soft core potential

[Ilya Chorny]

More specifically. My C12 term has a positive value. My C6 term is 0. I
am only concerned with the C12 term which is 
C12/(alpha*sigma^6*lambda^2+r^6)^2 
but the sigma value must be C12/C6 which if C6 was zero would blow up.
Does gromacs set the C6 value to sc_sigma^6.

Ilya


If the soft core used a value of zero then it would blow up. What 
On Mon, 2003-10-06 at 13:37, Erik Lindahl wrote:
> Hi,
> 
> As a said in the last paragraph - if c6=0 there isn't any dispersion 
> interaction at all, neither distorted or normal.
> 
> Just go back to the definition in section 4.3.1 of the manual. 
> Interactions are additive, so the formula holds true for the individual 
> dispersion and repulsion parts of the Lennard-Jones potential.
> 
> Cheers,
> 
> Erik
> 
> 
> 
> On Monday, October 6, 2003, at 01:11 PM, Ilya Chorny wrote:
> 
> > I don't understand. I'm am only interested in what happens to the
> > softcore distortion if C6 = 0. In  this case is sigma^6 = sc_sigma^6.
> >
> > Thanks
> >
> > Ilya
> >
> >
> >
> > On Mon, 2003-10-06 at 12:48, Erik Lindahl wrote:
> >> Hi,
> >>
> >> The softcore sigma value is used for the softcore distortion/scaling 
> >> of
> >> the potential, not the actual interaction.
> >>
> >> If both c6 & c12 are positive, it is calculated from sigma^6=c12/c6,
> >> otherwise the default value is used.
> >>
> >>
> >> Hence, If you have c6=0 for a particular interaction, the dispersion
> >> part will be zero no matter what the sc_sigma value is.
> >>
> >> Cheers,
> >>
> >> Erik
> >>
> >>
> >> On Monday, October 6, 2003, at 12:14 PM, Ilya Chorny wrote:
> >>
> >>> Hi I was wondering if anybody has an answer to my question?
> >>>
> >>> Ilya
> >>>
> >>> On Thu, 2003-10-02 at 10:11, Ilya Chorny wrote:
> >>>> Hello
> >>>>
> >>>> In the manual it says that by default sc_sigma = .3 nm.
> >>>> What C6 value does this correspond to. More specifically I have C6 
> >>>> set
> >>>> to 0.0. What will gromacs use as the C6 value in the soft core
> >>>> potential.
> >>>>
> >>>> Thanks
> >>>>
> >>>> Ilya
> >>>
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