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 independent-particle 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 non-linear 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.

We present a theoretical investigation of electronic and optical properties of free-base porphyrins based on density functional theory and many-body perturbation theory. The electronic levels of free-base porphine (H2P) and its phenyl derivative, free-base tetraphenylporphyrin (H2TPP) are calculated using the ab initio GW approximation for the self-energy. The approach is found to yield results that compare favorably with the available photoemission spectra. The excitonic nature of the optical peaks is revealed by solving the Bethe–Salpeter equation, which provides an accurate description of the experimental absorption spectra. The lowest triplet transition energies are in good agreement with the measured values.

We investigate the adsorption of Cs on the As-rich $c(2\mathrm{}\times 8)/(2\times 4)$ reconstruction of GaAs(001) at low coverages using a combination of theoretical and experimental techniques. Density-functional-theory local-density-approximation total-energy calculations and x-ray diffraction experiments find only minimal Cs-induced surface relaxation and identify three preferential adsorption sites within the partially disordered overlayer. These sites are, in order of decreasing occupation probability, the arsenic dimer bridge D site, the gallium dangling bond $T_2^{\prime }$ site, and the arsenic $T_3$ trench site. Detailed analysis of the wave functions and electronic charge densities allows us to clarify the bonding mechanisms at the three sites. At the gallium site, the bonding is strongly ionic and involves significant charge transfer to a new Cs-induced state reminiscent of the $p_z$ orbital of the gallium atom in the ${\mathrm{sp}}^{{}_2}$ configuration. In sharp contrast, at the arsenic sites, the charge transfer is minimal and the bonding rather occurs through mixing with a relatively delocalized state of the clean surface. The ionization energy decreases are estimated and compared for the three sites.