Note that the following color code has been used in this instruction sheet:

Broad headings are in red.

File names are in magenta.

Phrases to be typed into the command line are in blue.

Input parameters are in dark green.

A very brief reminder of useful linux commands:

In this exercise, you will first perform simple scf (self-consistent field) calculations on silicon.

You will see the following files:

day1_exercise1_instructions.html this file! this is a sample input file, for a primitive Si cell containing 2 atoms. this is a sample shell script that you can use (optionally) . this is an input file for an Si supercell containing 8 atoms. this is an input file for an Si supercell containing 16 atoms.

Si.pbe-rrkj.UPF this is the pseudopotential file.

For each calculation that you will run, you can use as a template that you can copy to another file and then edit. Alternatively, you can use shell scripts to automate this process.

The way to do this is:

pw.x < input_filename > output_filename

So in this particular case, you will type:

pw.x < > Si.sample.out

Vary the Monkhorst-Pack grid parameters nk1, nk2 and nk3.

You can do this either by manually editing input files, or by modifying the script

Use nk1=nk2=nk3= 1, 2, 3, 4, 5, 6.

Leave the offset at k1=k2=k3 = 1.

Remember: don't overwrite output files before you extract data from them!

Assemble the results for the dependence of total energy on lattice constant in a data file, e.g., one called etotvsalat.dat (2 columns, the first containing the lattice constant in bohr, and the second containing total energy in Ry).


When you run this, you will be prompted to supply:

The equivalence between supercell size and BZ sampling;

Let us now do a couple of calculations using supercells, i.e., unit cells that are larger than the primitive one.

(D) Some optional extra stuff :

If you finished all of the above stuff, and the instructor still hasn't moved on to the next exercise, you can (if you choose) do other things, e.g.: