Bulk silicon
============

This example shows how to run a calculation on bulk Si using various DFT codes,
including Quantum ESPRESSO, PARATEC, or Abinit. We also provide prebuilt 
mean-field calculations in the PREBUILD directory.

In this example, we compute the optical absorption spectrum of bulk Si and
plot the GW quasiparticle bandstructure. Note that BerkeleyGW allows you to
interpolate QP corrections with two different ways: either using Wannier functions
with the sig2wan code, or directly using the inteqp code, in the BSE folder.
We typically recommend users to use the inteqp code, since it's very stable,
fast, and easy to use. In this example, we show how to use both codes to produce
an interpolated quasiparticle bandstructure. Note that the Wannier interpolation
only works with the Quantum ESPRESSO mean-field code right now.

Note: the reference values were obtained with the Quantum ESPRESSO mean-field
code. Other mean-field codes will produces energies which should differ by
at most 10 meV.

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. Alternatively, you can also go to the PREBUILT folder and follow the
instructions to use pre-generated mean-field calculation from Quantum ESPRESSO.


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 7)
- Calculate self-energy corrections (directory 8)
- Generate electron-hole interaction kernel (directory 9)
- Solve BSE and calculate optical absorption (directory 10)


3. (Optional step) Here, we plot the GW bandstructure using Wannier
interpolation. This will only work if you used the ESPRESSO mean-field
starting point and if you have Wannier90 installed.
You should edit and submit `script_4`, and the resulting bandstructure
will be saved to `11-sig2wan/bandstructure_sig2wan.pdf`.
You must have python/matplotlib to run this step.


4. Here, we plot the GW bandstructure using the inteqp code.
This will work with any starting mean-field code.
You should edit and submit `script_5`, and the resulting bandstructure
will be saved to `12-inteqp/bandstructure_inteqp.pdf`.
You must have python/matplotlib to run this step.
