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.

The electron-phonon interaction and related transport properties are investigated in monolayer silicene and MoS${}_{2}$ by using a density functional theory calculation combined with a full-band Monte Carlo analysis. In the case of silicene, the results illustrate that the out-of-plane acoustic phonon mode may play the dominant role unlike its close relative, graphene. The small energy of this phonon mode, originating from the weak $sp$${}^{2}$ $$\pi${}$ bonding between Si atoms, contributes to the high scattering rate and significant degradation in electron transport. In MoS${}_{2}$, the longitudinal acoustic phonons show the strongest interaction with electrons. The key factor in this material appears to be the $Q$ valleys located between the $$\Gamma${}$ and $K$ points in the first Brillouin zone as they introduce additional intervalley scattering. The analysis also reveals the potential impact of extrinsic screening by other carriers and/or adjacent materials. Finally, the effective deformation potential constants are extracted for all relevant intrinsic electron-phonon scattering processes in both materials.

We present an efficient approach to describe the electronic transport properties of extended systems. The method is based on the surface Green’s function matching formalism and combines the iterative calculation of transfer matrices with the Landauer formula for the coherent conductance. The scheme is applicable to any general Hamiltonian that can be described within a localized orbital basis. As illustrative examples, we calculate transport properties for various ideal and mechanically deformed carbon nanotubes using realistic orthogonal and nonorthogonal tight-binding models. In particular, we observe that bent carbon nanotubes maintain their basic electrical properties even in the presence of large mechanical deformations.