QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.

Q uantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Q uantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

Quantum ESPRESSO is an open-source distribution of computer codes for quantum-mechanical materials modeling, based on density-functional theory, pseudopotentials, and plane waves, and renowned for its performance on a wide range of hardware architectures, from laptops to massively parallel computers, as well as for the breadth of its applications. In this paper, we present a motivation and brief review of the ongoing effort to port Quantum ESPRESSO onto heterogeneous architectures based on hardware accelerators, which will overcome the energy constraints that are currently hindering the way toward exascale computing.

We present a new scheme to study the linear response of crystals which combines the advantages of the dielectric-matrix and supercell (‘‘direct’’) approaches yet avoids many of their drawbacks. The numerical complexity of the algorithm is of the same order as that of a self-consistent calculation for the unperturbed system. The method is not restricted to local perturbations as the dielectric-matrix one nor to short wavelengths as the direct one. As an application, we calculate the long-wavelength optical phonons in Si and GaAs, both transverse and longitudinal, using norm-conserving pseudopotentials, and without any use of supercells.

The density-functional linear-response approach to lattice-dynamical calculations in semiconductors is presented in full detail. As an application, we calculate complete phonon dispersions for the elemental semiconductors Si and Ge, and for the III-V semiconductor compounds GaAs, AlAs, GaSb, and AlSb. Our results are in excellent agreement with experiments where available, and provide predictions where they are not. As a byproduct, we obtain real-space interatomic force constants for these materials, which are useful both for interpolating the dynamical matrices through the Brillouin zone, and as ingredients of approximate calculations for mixed systems such as alloys and microstructures. The possibility of studying these systems using the force constants of the pure materials relies on the so-called mass approximation, B i.e., on neglecting the dependence of the force constants upon composition. The accuracy of such an approximation is tested and found to be very good for cationic intermixing in binary semiconductors, while it is less so for anionic substitutions. The situation is intermediate in the case of elemental semiconductors.