Many-body perturbation theory calculations using the yambo code

Abstract

yambo is an open source project aimed at studying excited state properties of condensed matter systems from first principles using many-body methods. As input, yambo requires ground state electronic structure data as computed by density functional theory codes such as Quantum ESPRESSO and Abinit. yambo's capabilities include the calculation of linear response quantities (both independentparticle and including electron-hole interactions), quasi-particle corrections based on the GW formalism, optical absorption, and other spectroscopic quantities. Here we describe recent developments ranging from the inclusion of important but oft-neglected physical effects such as electron-phonon interactions to the implementation of a real-time propagation scheme for simulating linear and nonlinear optical properties. Improvements to numerical algorithms and the user interface are outlined. Particular emphasis is given to the new and efficient parallel structure that makes it possible to exploit modern high performance computing architectures. Finally, we demonstrate the possibility to automate workflows by interfacing with the yambopy and AiiDA software tools. CONTENTS

A monolayer transition-metal dichalcogenide as a topological excitonic insulator

“…The supercell size perpendicular to the T -MoS 2 layer was set to a z = 15.98Å and checked to be large enough to avoid spurious interactions with its replica.The equilibrium atomic lattice parameters were obtained by performing a full relaxation of the cell and atomic positions. The obtained equilibrium lattice parameters, a x = 5.74Å, a y = 3.19Å, as well as the Kohn-Sham electronic gap were in very good agreement with previous literature 2 .Many-body perturbation theory 4 calculations were performed using the Yambo code39,40 . Manybody corrections to the Kohn-Sham eigenvalues were calculated within the G0W 0 approximation to the self-energy operator, where the dynamic dielectric function was obtained within the plasmon-pole approximation41 .…”

Strain-induced effects on the electronic properties of 2D materials

“…52 Moreover, to guarantee the simulation of isolated layers, a cutoff in the bare Coulomb potential has also been used. 50,53 The k-point sampling was selected to be 42 Â 42 Â 1 in the BZ.…”

Ab initio modelling of local interfaces in doped organic semiconductors

“…69 In the periodic stacks the ground-state electronic structure is computed using the planewave pseudopotential code Quantum Espresso, 70,71 using a cutoff for the wave-functions (electron density) of 40 Ry (160 Ry), norm conserving pseudopotentials, 72 and a 1 Â 1 Â 12 k-grid. This is the starting point for the GW calculations performed with the code Yambo, 73,74 where the truncated Coulomb potential method 73,75 is adopted, defining a box-like region with a vertical dimension of 24 Å and a lateral size of 35 Å and 44 Å for 4T-F4TCNQ and 6T-F4TCNQ, respectively. The QP correction in the periodic stacks is calculated through the partially self-consistent G n W 0 approximation, where only the single particle Green's function G is updated at each iteration using the QP energies from the previous iteration with a convergence threshold of 10 meV.…”

“…The QP correction in the periodic stacks is calculated through the partially self-consistent G n W 0 approximation, where only the single particle Green's function G is updated at each iteration using the QP energies from the previous iteration with a convergence threshold of 10 meV. To improve the convergence of the self-energy with respect to the number of bands, the Bruneval-Gonze terminator technique 73 is adopted with 400 bands in total. The Godby-Needs plasmon-pole approximation 76 is employed to approximate the frequencydependence of the dielectric function, that is used to describe the screening function W 0 .…”