INSTRUCTIONS EXERCISE 4

Outline: Obtain the bandstructure, quantum conductance and density of states of a metallic (5,5) carbon nanotube
Input Files

Wannier Functions
In order to form localised WF that describe both the occupied and unoccupied In order to form localised WF that describe both the occupied and unoccupied pi and pi* manifolds, we use the disentanglement procedure to extract a smooth manifold of states that has dimension equal to 2.5 times the number of carbon atoms per unit cell. The positions of the energy windows are shown in the figure. The part of the wannier90 input file that controls the transport part of the calculation looks like:

transport = true
transport mode = bulk
one dim axis = z
dist cutoff = 5.5
fermi energy = -1.06
tran win min = -6.5
tran win max = 6.5
tran energy step = 0.01
dist cutoff mode = one dim
translation centre frac = 0.0 0.0 0.0

Descriptions of these and other keywords related to the calculation of transport properties can be found in the User Guide.

  1. Run pwscf and wannier90. Inspect the output file cnt55.wout. The minimisation of the spread occurs in a two-step procedure.
  2. Note that the initial pz projections on the carbon atoms are oriented in the radial direction with respect to the nanotube axis.
  3. The interpolated bandstructure is written to cnt55 band.agr (since bands_plot_format = xmgr in the input file).
  4. The quantum conductance and density of states are written to the files cnt55 qc.dat and cnt55 dos.dat, respectively. Note that this part of the calculation may take some time. You can follow its progress by monitoring the output to these files. Use a package such as gnuplot or xmgrace in order to visualise the data. You should get something that looks like this.