## What is the difference between Quantum ESPRESSO and VASP?

VASP is a commercial code and Quantum-Espresso (QE) is an open source code.

## How do I learn Quantum ESPRESSO?

- Visit youtube tutorial: https://www.youtube.com/channel/UCgQPek4ZSo_yL7wEjIhxvfA.
- Go through and follow quantum espresso tutorial PDFs.
- Explore and exercise on Energy calculation and Structure optimization (via by hand and automated) first.
- Find some publications/textbooks and learn how to interpret your data.

**How do you choose Pseudopotential in Quantum ESPRESSO?**

The choice depends heavily on the system of interest. A lot of benchmarks may help to choose but they are also limited by their choice of dataset. Therefore, the best way to choose a pseudo-potential should be reading literatures about calculations of systems similar to yours and using the most popular one.

### What is the meaning of smearing in Quantum ESPRESSO?

Smearing is a mathematical trick implemented in codes like quantum ESPRESSO so as to aid in convergence. It has no physical meaning.

### Is Quantum ESPRESSO free?

Quantum ESPRESSO is a suite for first-principles electronic-structure calculations and materials modeling, distributed for free and as free software under the GNU General Public License.

**How do you calculate Raman spectra in Quantum ESPRESSO?**

The procedure is as follows:

- Optimize the wavefunction by performing a self-consistent field (scf) calculation with pw. x code.
- Calculate the vibrational frequencies (normal modes/phonons) with ph. x code.
- Extract the phonon information from ph. x output using dynmat.
- Parse the dynmat.

#### What is pseudopotential Quantum Espresso?

Quantum ESPRESSO uses a unified PP format (UPF) for all types of PPs and still accepts a number of older formats. The directory upflib/ of the QE distribution contains utilities that convert to UPF format several PP formats used by other electronic-structure codes.

#### What is Alat in Quantum ESPRESSO?

In quantum espresso, ‘alat’ as written in the documentation is the ‘lattice constant’ of the system. So, far this is true for cubic system and it won’t affect either we input celldm(1) or A, B, C and cosine of angles as they will be the same (lattice constant).

**What is Gaussian smearing?**

If you are calculating a metal, you should use gaussian smearing. This smears out the fermi level, so that more of your k-points will be effectively on the fermi surface. The gaussian_smearing is specified in eV. If you are calculating an insulator, you should set gaussian_smearing to be some small value.

## What is Quantum ESPRESSO used for?

## Who developed Quantum ESPRESSO?

Giannozzi, S. Baroni, N. Bonini et al: Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials. Journal of Physics: Condensed Matter, 21, 39, 2009.