(8,0) semiconducting singled-wall carbon nanotube
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This example shows how to run a calculation on the (8,0) semiconduncting single-
wall carbon nanotube starting with either Quantum ESPRESSO or PARATEC for the
mean-field calculation.  We compute the GW quasiparticle corrections, the
optical absorption by solving the Bethe-Salpeter equation, and plot the
exciton wavefunction.


To run this example, follow the steps below.  Remember to modify each script
before launching it!


1. Enter your mean-field directory of choice (ESPRESSO, PARATEC, or ABINIT).
Read, customize and run/submit all scripts in that folder in the alphabetic order
they appear.  Note that we override the occupations in pp_in.  Quantum ESPRESSO
gives non-integer occupations for metals that may round to the incorrect
occupations. Suggested 1 node (tested with ncpu = 32, walltime = 00:10:00).


2. Go back to the directory containing this file, and modify/submit script_3.
Suggested 1 node (tested with ncpu = 32, walltime = 00:30:00).
We will:
- Generate dielectric matrix (directory 5)
- Calculate self-energy corrections (directory 6)
- Generate electron-hole interaction kernel (directory 7)
- Solve BSE, calculate optical absorption and plot the exciton WFN (directory 8)

You can plot the optical absorption spectrum in
`8-absorption/absorption_eh.dat` and `8-absorption/absorption_noeh.dat`,
and you can plot the exciton wavefunction in `8-absorption/xct000020.cube`
using software such as Vesta.
