Artem, Two things could be hindering your calculation. First, your mesh cutoff is quite low. I would use at least 200 Ry to get only decent results. In my experience with 300 Ry you get pretty good results for a graphitic system. Second, I don't see any k-point sampling along the ribbon length. This definitely could be the cause of your fluctuating dipole value.
Cheers, Marcos On Sat, Mar 13, 2010 at 3:08 AM, [email protected] <[email protected]> wrote: > Hi all! > I am a new user of Siesta and I'm involved in graphene band structure > calculations. I can not obtain the correct band structure for a graphene > nanoribon (N=3m+2, armchair passivated by H-atoms). Trying to do that I > was overwhelmed with the fact that the system absolutely symmetrical in > Y-axis (finite size, 5 honeycomb rings) has non-zero dipole moment along > Y-axix which depends sharply on the Meshcutoff value. > Could anyone explain me where it comes from? What are the possible sources > of this "effect" and how it may affect the band structure? > > The replica of my .fdf and .out files are attached below. > > Thanks for any reasonable help. > > From input-file > > NumberOfAtoms 26 > NumberOfSpecies 2 > > %block ChemicalSpeciesLabel > 1 6 C # Species index, atomic number, species label > 2 1 H > %endblock ChemicalSpeciesLabel > Meshcutoff 100.00 Ry > LongOutput T > WriteDenchar T > AtomicCoordinatesFormat Ang > %block AtomicCoordinatesAndAtomicSpecies > 0.00 7.37853644 0.000 1 > 1.42 7.37853644 0.000 1 > -0.71 6.148780367 0.000 1 > 2.13 6.148780367 0.000 1 > 0.00 4.919024294 0.000 1 > 1.42 4.919024294 0.000 1 > -0.71 3.68926822 0.000 1 > 2.13 3.68926822 0.000 1 > 0.00 2.459512147 0.000 1 > 1.42 2.459512147 0.000 1 > -0.71 1.229756073 0.000 1 > 2.13 1.229756073 0.000 1 > 0.00 0.00 0.000 1 > 1.42 0.00 0.000 1 > -0.71 -1.229756073 0.000 1 > 2.13 -1.229756073 0.000 1 > 0.00 -2.459512147 0.000 1 > 1.42 -2.459512147 0.000 1 > -0.71 -3.68926822 0.000 1 > 2.13 -3.68926822 0.000 1 > 0.00 -4.919024294 0.000 1 > 1.42 -4.919024294 0.000 1 > 0.00 5.889024294 0.000 2 > 0.00 -5.889024294 0.000 2 > 1.42 5.889024294 0.000 2 > 1.42 -5.889024294 0.000 2 > %endblock AtomicCoordinatesAndAtomicSpecies > > %block PAO.BasisSizes > C DZP > H DZP > %endblock PAO.BasisSizes > > LatticeConstant 2.459512147 Ang > %block LatticeVectors > 1.732050808 0.00 0.0 > 0.0 80.0 0.0 > 0.0 0.00 80.0 > > %endblock LatticeVectors > > %block BandLines > 1 -1.0 0.0 0.0 > 20 0.0 0.0 0.0 > 20 1.0 0.0 0.0 > %endblock BandLines > > > From out-file > > siesta: Electric dipole (a.u.) = 0.000000 17.412033 0.000000 > siesta: Electric dipole (Debye) = 0.000000 44.257004 0.000000 > > > Artem Baskin, > PhD student, > University of Illinois at Chicago > > >
