Hi Steven, On Aug 3 2007, Steven G. Johnson wrote:
>On Wed, 1 Aug 2007, F.S.F. Brossard wrote: >> I am trying to define a structure with a defect and eventually look at >> the Q. However, I already obtain inconsistent results in the defined >> perfect crystal depending on whether I set the symmetry or not (please >> see attachments). One would expect half a hole at all sides of the cell, >> not just two of them (in the case without defined symmetry). Hence we >> should have 8 periods in the (1 0) direction. I assume setting the >> symmetry takes the mirror symmetry of the two sides without the >> additional half-hole, hence we end-up with 6 periods instead of the >> expected 8. Thanks for any advice or solution to this problem. > >The problem is that your structure, without symmetry, is not symmetric. >Hence when you impose symmetry you get a different results. > >The reason it is not symmetric is that >geometric-objects-lattice-duplicates was really designed for MPB, where we >always have periodic structures. Therefore, it only puts objects on one >side of the boundary, assuming they will wrap around. However, in your >Meep simulation you are *not* using periodic boundaries, so the objects >don't wrap around. You can set periodic boundaries by doing > (set! k-point (vector3 0 0 0)) >in which case you will get the structure you expect to see. (Note that it >is perfectly possible to use both periodic boundaries and PML at the same >time.) > >If you don't have/want periodic boundaries, then you probably shouldn't be >using geometric-objects-lattice-duplicates. Instead, use >geometric-objects-duplicates, which gives you more control over how many >duplicates you have and where they are placed. > >Regards, >Steven G. Johnson Yes, I have recently switched to geometric-objects-duplicates only and have no more problem with that. Thanks, Fred -- Frederic Brossard Hitachi Cambridge Laboratory Cavendish Laboratory J J Thomson Avenue Cambridge CB3 0HE _______________________________________________ meep-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/meep-discuss
