Quantum ESPRESSO (Quantum Open-Source Package for Research in Electronic Structure, Simulation, and Optimization; QE)[2][3] 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.

It is based on density functional theory (DFT), plane wave basis sets, and pseudopotentials (both norm-conserving and ultrasoft).

The basic packages include Pwscf,[4] which solves the self-consistent Kohn-Sham equations, obtained for a periodic solid, CP to carry out Car-Parrinello molecular dynamics, and PostProc, which allows data analysis and plotting.

Noteworthy additional packages include atomic for pseudopotential generation, PHonon for density-functional perturbation theory (DFPT) and the calculation of second- and third-order derivatives of the energy with respect to atomic displacements, and NEB (nudged elastic band) for the calculation of reaction pathways and energy barriers.

The different tasks that can be performed include The main components of the Quantum ESPRESSO distribution are designed to exploit the architecture of today's supercomputers, which are characterized by multiple levels and layers of inter-processor communication.