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
