Re: [ESPResSo-users] magnetic field due to magnetic dipoles

[Olaf Lenz]

Hi!

On 11/09/2012 04:51 PM, tomaž mohorič wrote:
> In my case I would like to know what is the magnetic field (due to
> all other dipoles) at the position of each particle. Problem is not
> so trivial, since the magnetic field due to magnetic dipole decreases
> as 1/r**3 and one should take into account contribution from all
> particles (for beginning I assume repeating cells in x and y axis).

ESPResSo does exactly that: it computes the force acting on a dipole
caused by all other dipoles, using the P3M algorithm
(http://en.wikipedia.org/wiki/P3M).

> My question is: is there any way to obtain the magnetic field due to 
> magnetic dipoles from Espresso?

Even though it does of course compute it, the software does not allow to
read out the magnetic field at the particle positions at the moment - it
is only implicitly contained in the forces and torques acting on the
dipoles.
However, it should not be very hard to modify the C code such that it
also prints out the fields, or even puts it into a Tcl variable - if you
understand how the algorithm works. Have a look at the file
src/p3m-dipolar.c in the ESPResSo code. Note that you will have to
output both the near-field and the k-space part.

In general, we should probably be thinking about a concept how to access
the various force components, but that will definitely take a while.

Olaf

-- 
Dr. rer. nat. Olaf Lenz
Institut für Computerphysik, Allmandring 3, D-70569 Stuttgart
Phone: +49-711-685-63607

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