Hi Marcos Thank a lot, Gregorio
> Hi Gregorio, > > On Thu, Jan 7, 2010 at 1:02 PM, <[email protected]> wrote: >> I am a new user of SIESTA. > > It's ok, everyone has been one at some point :D > >> I am trying to calculated the band structure a >> pi-conjugated polymer. I have searched in the SIESTA-L, I have found >> that >> I need a blocklabel such as >> >> BandLinesScale ReciprocalLatticeVectors >> >> %block BandLines >> 1 0.0 0.0 0.0 # Gamma-point >> 20 0.5 0.0 0.0 # X-point >> etc >> %endblock BandLines >> >> I have to add: >> WriteBands True > > If the manual says so... (really, I don't remember it by heart). > >> >> I have some questions: >> >> 1)I noted that BandLinesScales can be scaled by ReciprocalLatticeVectors >> or pi/2, which is the differece? > > A huge one when it comes to specifying the points to be plotted, but > the results are the same. For the first, you can determine at which > points your band structure will be written as a fraction of the > reciprocal lattice vectors themselves, whereas in the second, you will > have actual cartesian coordinates in k-space, but scaled by the factor > pi/a. As an example, suppose you have a 2D cell in real space with > LatticeConstant A, such that > > > LatticeConstant A Ang > %block LatticeVectors > 1.000 0.000 0.000 > 0.000 5.000 0.000 > 0.000 0.000 50.000 > %endblock LatticeVectors > > The reciprocal lattice vectors as siesta calculates would then be > > b1=(2*pi/A,0) and b2=(0,2*pi/5A) > > (b3 is close to zero, so I won't take it into account from now on). So > now suppose that the points of interest to you are the middle of the > largest side **of the BZ** (let's call it M), one of its corners > (let's call it Y), and the Gamma point. In the first case > (ReciprocalLatticeVectors), these three coordinates can be written as > > Gamma=(0,0) > M=(0.5,0) > Y=(0.5,0.5) > > (remember that the Brillouin zone is the Wigner-Seitz cell in > reciprocal space!). In the second case (scaled by pi/A), you'd have > > Gamma=(0,0) > M=(1.,0) > Y=(1.0,1/5) > > get it? It's just two different ways of expressing the same thing, > whatever is easier for you. Often it is easier to use the fractional > coordinates in k-space (ReciprocalLatticeVectors). > >> >> 2) The first colum indicates the grid between two consecutive points. >> How >> Can I know what value Must I use? >> What k-points (gamma, x, L, etc) Must I use? >> >> Does it related with WirteKpoints, WreteEigenvalues and Writekbands? >> > > That depends on the symmetry of your system. In your case, plotting a > band structure only makes sense if you have a crystal or an infinte > polymer chain - in this latter case, all you have to do is plot the > structure along the reciprocal lattice vector corresponding to the > polymer chain's length. There are some internet resources on > crystallography that give you a set of high-symmetry k-points for many > lattices, I think the Bilbao Crystallographic Server is completely > open for everyone. > >> 3) Finally. I know about GnuPlot, Does anyone tell me some program for >> view the band structures? Does some program for Windows operative >> system? > > Gnuplot for Windows? :) (It does exist...) > > Check the siesta documentation for the bands files, it's pretty > straightforward to plot them using gnuplot. > > Marcos >
