Hi, The reason you need different parameters for zigzag and armchair nanotubes is that the zigzag are semiconducting whereas the armchair are metallic. So it is reasonable that you have to use a bigger number of k points to integrate the Brillouin zone in the last case.
For armchair NT I relaxed the structure and the unit cell starting with 2 k points and then I increased the k points (relaxing the whole structure again) until the result was converged. If you want ot obtain a "proper" DOS you have to use a small lorentzian width (0.01) and at least 80 k-points to get rid of oscillations and spurious peaks. Regarding the optimization with 2 uc, if you optimize the structure for 1 uc with a certain number of k-point you can use that optimize coordinates, reapeat them using the optimized lattice vectors and use half the number of k-points. You do not have to relax them again. Regards Victor ------------------------------------------------------------- Victor Manuel Garcia Suarez Research Assistant | Tlf: 0044 - (0)1524 593 995 Physics Department | Fax: 0044 - (0)1524 844 037 Lancaster University | e-m: [EMAIL PROTECTED] Lancaster LA1 4YB | [EMAIL PROTECTED] United Kingdom | www: http://condmat.uniovi.es/victor ------------------------------------------------------------- -----Original Message----- From: Siesta, Self-Consistent DFT LCAO program, http://www.uam.es/siesta on behalf of navaratnarajah kuganathan Sent: Wed 6/1/2005 16:47 To: [email protected] Subject: [SIESTA-L] Nanotube Dear All, I am a new student to the field of calculation on carbon nanotube using SIESTA.I would like to have a 2unit cell optimised structure of carbonnanotube for 10-10 tube.I have already done 2 unit cell optimisation for zigzag nanotube .My procedure was as follows. 1 Geometry optimisation with mesh 250 Ry and with that optimised coordinates I optimised mesh seeing the total energy (No geometry optimisation CG=0).In this case I have not used any k points. 2.Then with the optimised mesh and coordinates I have started k point optimisation(using block monkhorstpack and No geometry optimisation CG=0).Then I found the required k points 10.Then I have done 1 k point variable relaxation . 3.With the coordinates and lattice parameters ,I did Fixed geometry optimisation using 10 k points. 4.Finally with the optimised coordinates I did Variable cell realxation . Fianlly I obtained the good Density of states plot and band structures for this unit cell relaxation..Like wise I have done optimisation for 2 unit cell calcualtion generating the coordinates from the final variable relaxation.Here also I obtained the good DOS and band structures. When I was doing calcualtion for zig zag tube I observed the final pressure for 1 unitcell fixed relaxation was -4.0569 Kbar.Then it was reduced to -0.0004 when doing va riable cell relaxation But When I am doing the calcualtion using the same procedure for 10-10 tube I couldnot find any good DOS and band structure for 1 unit cell.I have not done for 2 unitcell calcualtion.In this case pressure was -104.7488 for fixed relaxation . Interestingly when I tried putting 280 Mesh and 60k points for 10-10 tube (just putting all the values in the same input file ,see the input below) I got the very good band structures and DOS.Can I generate the coordinates for 2 Unit cell calculation ?.Any one who has done this type of calcualtion is required to help in this regard. SIncerely Kugan #FDF file for 10-10 nanotube #NumCG =50!!! SystemName 10-10 tube SystemLabel SWNT_10_10 NumberOfAtoms 40 # Number of atoms NumberOfSpecies 1 %block ChemicalSpeciesLabel 1 6 C %endblock ChemicalSpeciesLabel PAO.Basis < C_Basis.fdf # contains optimized basis # Lattice, coordinates, k-sampling LatticeConstant 1.00 Ang %block LatticeVectors 25.000000 0.000000 0.0000000 0.0000000 2.514900 0.0000000 0.0000000 0.000000 25.000000 %endblock LatticeVectors %block ProjectedDensityOfStates -20.0 10.00 0.200 500 eV %endblock ProjectedDensityOfStates #kgrid_cutoff 0.0 Bohr # not used as kgrid_Monkhorst_Pack is specified %block kgrid_Monkhorst_Pack 1 0 0 0.0 0 60 0 0.0 0 0 1 0.0 %endblock kgrid_Monkhorst_Pack WriteBands .true. BandLinesScale ReciprocalLatticeVectors %block BandLines 1 0.0 0.0 0.0 \Gamma 45 0.0 1.0 0.0 X %endblock BandLines SolutionMethod diagon ElectronicTemperature 300.0 K # default = 300 K AtomCoorFormatOut Ang # DFT, Grid, SCF XC.functional LDA # Exchange-correlation functional type XC.authors CA # Particular parametrization of xc func SpinPolarized F # Spin unpolarized calculation MeshCutoff 280. Ry # Equivalent planewave cutoff for the grid MaxSCFIterations 200 # Maximum number of SCF iterations per step DM.MixingWeight 0.3 # New DM amount for next SCF cycle DM.Tolerance 1.d-4 # Tolerance in maximum difference # between input and output DM DM.NumberPulay 3 # Number of SCF steps between pulay mixing # Molecular dynamics and relaxations MD.TypeOfRun cg # Type of dynamics: MD.VariableCell F MD.NumCGSteps 300 MD.MaxStressTol 0.02 GPa MD.MaxForceTol 0.04 eV/Ang MD.TargetPressure 0.00 GPa # Output options WriteCoorInitial T WriteCoorStep T # must be set false to write coords at each relax step to .ANI file WriteForces T WriteKpoints F WriteEigenvalues F # use with eig2dos to plot density of states WriteKbands F WriteBands F WriteMullikenPop 0 # Write Mulliken Population Analysis WriteCoorXmol F WriteCoorCerius F # writes final coordinats for Cerius WriteMDCoorXmol F WriteDM T # true is default - allows for a restart using DM from previous run WriteMDhistory F WriteCoorXmol F # Options for saving/reading information DM.UseSaveDM T # Use DM Continuation files (use for restarting jobs) MD.UseSaveXV T # Use stored positions and velocities (use for restart jobs) UseSaveData T # useful if a restart is needed MD.UseSaveCG T # Use stored positions and velocities SaveRho F # Write valence pseudocharge at the mesh SaveDeltaRho F # Write RHOscf-RHOatm at the mesh SaveElectrostaticPotential F # Write the total elect. pot. at the mesh SaveTotalPotential F # Write the total pot. at the mesh WriteSiestaDim F # Write minimum dim to siesta.h and stop WriteDenchar F # Write information for DENCHAR AtomicCoordinatesFormat NotScaledCartesianAng %block AtomicCoordinatesAndAtomicSpecies 9.680181 0.628716 18.833418 1 11.058592 0.628716 19.281291 1 6.496028 0.628716 15.966395 1 7.347933 0.628716 17.138942 1 5.605189 0.628716 11.775326 1 5.605189 0.628716 13.224674 1 7.347933 0.628716 7.861058 1 6.496028 0.628716 9.033605 1 11.058592 0.628716 5.718709 1 9.680181 0.628716 6.166582 1 15.319819 0.628716 6.166582 1 13.941408 0.628716 5.718709 1 18.503972 0.628716 9.033605 1 17.652067 0.628716 7.861058 1 19.394811 0.628716 13.224674 1 19.394811 0.628716 11.775326 1 17.652067 0.628716 17.138942 1 18.503972 0.628716 15.966395 1 13.941408 0.628716 19.281291 1 15.319819 0.628716 18.833418 1 9.033605 1.886184 18.503972 1 11.775326 1.886184 19.394811 1 6.166582 1.886184 15.319819 1 7.861058 1.886184 17.652067 1 5.718709 1.886184 11.058592 1 5.718709 1.886184 13.941408 1 7.861058 1.886184 7.347933 1 6.166582 1.886184 9.680181 1 11.775326 1.886184 5.605189 1 9.033605 1.886184 6.496028 1 15.966395 1.886184 6.496028 1 13.224674 1.886184 5.605189 1 18.833418 1.886184 9.680181 1 17.138942 1.886184 7.347933 1 19.281291 1.886184 13.941408 1 19.281291 1.886184 11.058592 1 17.138942 1.886184 17.652067 1 18.833418 1.886184 15.319819 1 13.224674 1.886184 19.394811 1 15.966395 1.886184 18.503972 1 %endblock AtomicCoordinatesAndAtomicSpecies __________________________________________________ Do You Yahoo!? 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