Re: [ESPResSo-devel] Local stress tensor/Multibody interaction and A bug in tensor distribute

[Christoph Junghans]

Hi Zunjing,

> 1) Checking with the newest released version Espresso-2.1.2j, I found that
> it does not include any 3-body or higher-order interactions, eg. Angle
> bending, Dihedrals. Has any Espresso developer ever coded this part? If not,
> then when involving any three-body interactions, how reliable about the
> results of stress tensor with current Espresso?

I guess the main point was that the angle bending doesn't contribute  
to the pressure. And that is why nobody has implemented the virials  
for these interactions till now. It will depend very much on the  
system you study how reliable the results are without these  
contributions.

> Does anyone know that who coded this part and how this value "0.0000000001"
> was decided? Will it be effected by compiler or machine? For my system, this
> value "0.0000000001" sounds too small, leading to crash of Espresso when
> computing local stress tensor.

Ben has implemented the local stress tensor in Sept 2007. And this is  
a feature not a bug!  It seem like something went wrong in the case of  
your simulation. Ok "0.0000000001" is not the best choice. It should  
be ROUND_ERROR_PREC (see config.h) instead, which is 1e-14 by default  
and even smaller.

Cheers,

Christoph

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