Erkan, If you multiply 24.9 by 0.1704, you get roughly the value of cell_length_c that tubegen gives you. Now, I don't know what tubegen does, but the large values of the lattice vectors in the ab plane are meant to give a good distance between the tube and its images - siesta uses periodic boundary conditions and the largest possible distance is necessary to avoid the above mentioned interactions.
Marcos On Wed, May 5, 2010 at 9:04 PM, Erkan Tetik <[email protected]> wrote: > Dear all, > > I want to calculate a cabon nanotube with siesta and I've tried the > "nanotube-c-5-0" example that it is in the Tests folder in Siesta. But, I > don't understand the LatticeVectors and LatticeConstant parameter in the fdf > file for this calculation only. I use the "tubegen" program to generate > anything carbon nanotube. For example, I'm getting the Atomic Coordinates > and lattice constats for CNT(5,0) with tubegen, I mean; > > lattice constats(unit is Angs, tubegen out file); > _cell_length_a 7.3128 > _cell_length_b 7.3128 > _cell_length_c 4.2806 > > in the nanotube-c-5-0.fdf file; > LatticeConstant 24.9 Ang > %block LatticeVectors > 1.0 0.0000 0.0 > -0.50 0.86602540378444 0.00 > 0.0 0.0 0.1704 > %endblock LatticeVectors > > I haven't obtained the LatticeConstant and LatticeVectors in the > nanotube-c-5-0.fdf by using the lattice constats in the tubegen out file. I > have been examined the siesta-3.0-b.pdf file, but, I could not find a > solution yet. Please, could you explain to me? > > Best Regards. > Erkan Tetik >
