[MMTK] Bug in MMTK.Universe.largestDistance()?

Andreas Kring akring1729 at gmail.com
Mon Jan 7 09:23:26 UTC 2008


Konrad Hinsen skrev:
> On 04.01.2008, at 13:11, Andreas Kring wrote:
> 
>> I think there is a bug in MMTK.Universe.largestDistance(). An example of
>> the error can be seen in the script below.
> 
> There is indeed a bug, but it is not where you think it is. The 
> calculation for orthogonal universes (including cubic ones) is correct, 
> but the one for non-orthogonal boxes isn't.
> 
> What largestDistance() should return is the largest interparticle 
> distance that can be represented in the universe independent of 
> orientation. In other words, the largest distance L is defined as the 
> largest L such that an atom A2 placed at a distance L from a given atom 
> A1 in an arbitrarily chosen direction will
> make the minimum-image distance between A1 and A2 equal to L. For a 
> rectangular box, this makes L equal to half the shortest edge length.
> 
> This method is used in MMTK for checking cutoff radii for particle 
> interactions. For consistency, all real-space cutoffs should be less 
> than the number returned by universe.largestDistance(). For any larger 
> cutoff, the effective interaction volume of each atom is no longer 
> spherical.
> 

Ok, I miss understood what the method does - thanks for clarifying this.

Kind regards
Andreas



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