Quantum Espresso (QE) is an integrated suite of Open-Source computer codes for electronic-structure calculations and materials modeling. It is based on density-functional theory, plane waves, and pseudopotentials. In this set of tutorials, you will learn how to run the essential calculations based on density functional theory as implemented in QE on JHU-MARCC, a shared computing facility. You can practice running calculations in various listed topics starting with a test run.
QE is an Open Source distribution. The primary references of the QE code are the articles:
P. Giannozzi et al., J. Phys.: Condens. Matter 21, 395502 (2009)
P. Giannozzi et al., J. Phys.: Condens. Matter 29, 465901 (2017)
- How to Configure (pdf download)
- Input and Convergence Parameters (pdf download)
- Test Run (pdf download)
In this tutorial we will prepare a simple job and execute it on JHU-MARCC. The goal is to make sure that we have configured Quantum Espresso properly and everything runs well. We will run a simple total energy calculation (scf calculation) for silicon in the diamond structure. We will also learn how to use the command line to create an input ﬁle and a job submission file to submit our job to the queue.
- Convergence Parameters of DFT Calculations (pdf download)
In this tutorial we will explore two important convergence parameters of DFT calculations, the planewave kinetic energy cutoﬀ ecutwfc, and the Brillouin zone sampling k-points. As an example, for silicon, we study how the total energy, the number of planewaves, and the timing vary as a function of the planewaves cutoﬀ ecutwfc, and how the total energy of silicon varies with the number of k-points. As an exercise, we also explore the scaling of DFT calculations as a function of system size.
- Equilibrium Structure of a Diatomic Molecule and a Bulk Crystal (pdf download)
Among all possible structures, the equilibrium structure at zero temperature and zero pressure is found by minimizing the DFT total energy. In this tutorial we will learn the concept of calculating the equilibrium structure. We will calculate 1) the equilibrium structure and the binding energy of a diatomic molecule using the Cl2 molecule as an example, 2) the equilibrium structure and the cohesive energy of a bulk crystal using silicon, and 3) the equilibrium lattice parameter of silicon, diamond, and graphite.
- Automatic Optimization of Crystal Structure and Elastic Constant (pdf download)
In this tutorial we will 1) automatically optimize the atomic coordinates by using calculation type relax and 2) automatically optimize the unit cell by using calculation type vc-relax. We will then familiarize ourselves with calculation of bulk modulus and the elastic constant, using diamond as a test case. As an exercise, we will set up a new calculation on SrTiO3 starting with a simple input ﬁle for the material. To ﬁnd the initial geometry for the unit cell and atomic coordinates, we search the Materials Project Database.
- Phonon Dispersion (pdf download)
In this tutorial we will learn how to calculate 1) the vibrational frequencies of a diatomic molecule, Cl2, 2) phonon dispersion relations of diamond, GaAs, and SrTiO3, and 3) LO-TO splitting, IR activity, and low-frequency dielectric constants of a polar semiconductor, GaAs.
- Band Structure and UV/VIS Spectra (pdf download)
In this tutorial we will explore how to 1) calculate the band structure and visualize the wavefunctions corresponding to selected Kohn-Sham eigenvalues of silicon, and 2) calculate the band structure and the corresponding optical absorption spectrum (UV/Vis spectra) of GaAs to obtain the imaginary part of the dielectric function, e2(ω), which is related to the optical absorption coeﬃcient κ(ω).