  Quantum 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
pseudo-potential and projector-augmented-wave approaches. Quantum 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 theirs 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.
