[gmx-users] System size and minimum image convention

Justin Lemkul jalemkul at vt.edu
Fri Feb 22 00:16:43 CET 2013

On 2/21/13 6:10 PM, Elisabeth wrote:
> Hello everyone,
> Does anyone know if the minimum image convention has something to do with
> the box size effect (independence of simulation results from system size) ?
> i.e. When the box size is larger than 2*r_c, does this ensure that the
> results are independent of size pf the system (number of atoms in box)?
> Please guide me if I am confusing these two issues with each other,

The finite size effect and minimum image convention are different.  The minimum 
image convention simply says that your molecules should not have their forces 
double-counted through interactions in the central unit cell and a neighboring 
one.  That leads to spurious dynamics.  A box of 2*r_c is an absolute minimum, 
but if there is a solute involved (i.e. not pure solvent) then your box must be 
larger (diameter of solute + 2*r_c).



Justin A. Lemkul, Ph.D.
Research Scientist
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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