DFT_esercitazioni

Beginner tutorial for Density Functional Theory(DFT) calculation using Quantum Espresso(QE)[1,2]

Required packages

• A working version of QE needs to be installed/compiled and the executables needs to be located in the PATH environmental variable or specified manually in the variable BIN_DIR.
• A working version of gnuplot (>=5.0) (The exercises script will generate gnuplot file to plot the results. Other programs can also be used)
• A working version of XCrySDen, a program that can visualize input and output files of QE.

Installing/Compiling QE

• QE can be installed from repository for Debian based linux distros (e.g.: Ubuntu) by running the command

  sudo apt-get install quantum-espresso
  

  PS: The max version of QE that can be installed this way is ... maybe 6.0 now

• QE can be compiled from source:

1. Download the desired release version from the GitHub page "https://github.com/QEF/q-e/releases".

2. Unzip/tar the downloaded package and go inside the folder.

3. From terminal run the commands

   ./configure --prefix=path for installation
   make all
   make install
   

NOTES: options for the configuration / use of external libraries for optimized executables is beyond the purpose of this tutorial.

Exercises and their purpose/aim

Bulk silicon (0_Si_bulk)

1. Construct an input file for a choosen system and visualize it using xcrysden
2. Run a simple self-consistent calculation using pw.x
3. Estimate the kinetic cutoff convergency
4. Determine the theoretical lattice parameter
5. Calculate a charge density and visualize it using XCrySDen
6. Generate a high-symmetry k-path using xcrysden and calculate a band structure
7. Calculate the density of states(DOS) and optical properties(independent particle approximation) and show the convergence over the number of k_points and empty bands used

Two-dimensional boron nitride (1_BN)

1. How to use a supercell in order to run calculation for material that are not periodic in all directions.

Graphene (2_Graphene)

1. Run calculation for a metallic/semimetallic system

Carbon monoxide (3_CO)

1. Run a relax calculation and visualize the output using xcrysden
2. Run a calculaiton for a molecule (0D system)
3. Calculate the binding energy of a molecule
4. Visualize the HOMO and LUMO of a molecule (charge density for specific k-point and band)
5. Use a Lennard-Jones like potential to fit the data 'E_tot' vs 'bond lenght'

Other folders

• Docs: Contain additional tutorials in pdf format
• Codes: Contain user-made code to analyze some of the data produced by QE
  1. boad.c (by Davide Grassano aka Crivella): Apply a gaussian broadening(to the y_n data) to a multicolumn file where the 1st column represents the x data and the 2nd,3rd,... columns represent the y_1, y_2, ... data.
  2. plot_pwbands.f90 (by ...) : ...
• Pseudo: Contain the pseudopotential required to perform the exercises

Bibliography

1. P. Giannozzi, S. Baroni, N. Bonini, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, G. L. Chiarotti, M. Cococcioni, I. Dabo, et al., Journal of physics: Condensed matter 21, 395502 (2009).
2. P. Giannozzi, O. Andreussi, T. Brumme, O. Bunau, M. B. Nardelli, M. Calandra, R. Car, C. Cavazzoni, D. Ceresoli, M. Cococcioni, et al., Journal of Physics: Condensed Matter 29, 465901 (2017).