[gmx-users] Why density increase with increasing the cutoff length?

[XAvier Periole]

> From what my Professor told me it is my understanding that cutoff  
> length is somewhat a trade-off between accuracy of the simulation  
> and length of time to generate the simulation. A higher cut-off  
> indicates more accuracy but will take longer to simulate. I use low  
> cut-offs for less important simulations like energy minimizations.
>
> An increase in density would mean a larger number of simulated  
> molecules and therefore a need for a higher cut-off for more  
> accurate data. That is my best theory anyway.
This point of view implies that the potentials used are perfect and  
then indeed the
longer cutoff you use the more accurate your interactions energies  
become.
You have to consider that current potential are parameterized to  
reproduce some
data (structural and thermodynamics experimental data) and this using a
given cutoff. Modifying the cutoff means that you modify the potential  
and
therefore the model will not necessarily (and most often) fit the  
experimental
data anymore.
>
> Arden Perkins
>
> On Sun, Dec 20, 2009 at 11:03 PM, Yanmei Song <ysong30 at asu.edu> wrote:
> Dear Users:
>
> Anyone can explain why the density of the water models increase with  
> increase the cutoff length. I tried a couple water models in  
> reaction-field, PME simulations.The cutoff length ranged from 0.9 to  
> 1.5. They all show the same trend. Then there must be some reasons.  
> Anyone can tell me why?
>
> -- 
> Yanmei Song
> Ph.D. Candidate
> Department of Chemical Engineering
> Arizona State University
>
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