Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, selected columns of the density matrix) and the ability to calculate new properties (shift currents and Berry-curvature dipole, and a new interface to many-body perturbation theory); performance improvements, including parallelisation of the core code; enhancements in functionality (support for spinor-valued Wannier functions, more accurate methods to interpolate quantities in the Brillouin zone); improved usability (improved plotting routines, integration with high-throughput automation frameworks), as well as the implementation of modern software engineering practices (unit testing, continuous integration, and automatic source-code documentation). These new features, capabilities, and code development model aim to further sustain and expand the community uptake and range of applicability, that nowadays spans complex and accurate dielectric, electronic, magnetic, optical, topological and transport properties of materials.

The mechanism for the ferromagnetic order of (Ga,Mn)As and (Ga,Mn)$\mathrm{N}$ is extensively studied over a vast range of Mn concentrations. We calculate the electronic structures of these materials using density functional theory in both the local spin density approximation (LSDA) and the local density approximation $\left(\mathrm{LDA}\right)+U$ scheme, that we have now implemented in the code SIESTA. For (Ga,Mn)As, the $\mathrm{LDA}+U$ approach leads to a hole mediated picture of the ferromagnetism, with an exchange constant $N\beta =-2.8\mathrm{eV}$. This is smaller than that obtained with LSDA, which overestimates the exchange coupling between Mn ions and the As $p$ holes. In contrast, the ferromagnetism in wurtzite (Ga,Mn)$\mathrm{N}$ is caused by the double-exchange mechanism, since a hole of strong $d$ character is found at the Fermi level in both the LSDA and the $\mathrm{LDA}+U$ approaches. In this case the coupling between the Mn ions decays rapidly with the Mn-Mn separation. This suggests a two phases picture of the ferromagnetic order in (Ga, Mn)$\mathrm{N}$, with a robust ferromagnetic phase at large Mn concentration coexisting with a diluted weak ferromagnetic phase.

This work reports on the high power conversion efficiency (PCE) and high open circuit voltage (V_oc) of bromide-based quasi 2D perovskite solar cells. A V_oc of more than 1.4 V and, at the same time, a PCE of 9.5% for cells with hole transport material (HTM) were displayed, whereas a V_oc value of 1.37 V and a PCE of 7.9% were achieved for HTM-free cells. Bromide quasi 2D perovskites were synthesized using various long organic barriers (e.g., benzyl ammonium, BA; phenylethyl ammonium, PEA; and propyl phenyl ammonium, PPA). The influence of different barrier molecules on the quasi 2D perovskite's properties was studied using absorbance, X-ray diffraction, and scanning electron microscopy. No change was observed in the exciton binding energy as a result of changing the barrier molecule. Density functional theory (DFT) with spin–orbit coupling calculations showed that in the case of BA, holes are delocalized over the whole molecule, whereas for PEA and PPA, they are delocalized more at the phenyl ring. This factor influences the electrical conductivity of holes, which is highest for BA in comparison with the other barriers. In the case of electrons, the energy onset for the nonzero conductivity is lowest for BA. Both calculations support the better PV performance observed for the quasi 2D perovskite based on BA as the barrier. Finally, using contact angle measurements, it was shown that the quasi 2D perovskite is more hydrophobic than the 3D perovskite. Stability measurements showed that cells based on the quasi 2D perovskite are more stable than cells based on the 3D perovskite.

An ab initio study of the role of electronic curve crossing in the photodissociation dynamics of the alkyl halides is presented. Recent experimental studies show that curve crossing plays a deterministic role in deciding the channel of dissociation. Coupled repulsive potential energy curves of the low-lying ${\mathrm{n-\sigma }}^{*}$ states are studied including spin–orbit and relativistic effects. Basis set including effect of core correlation is used. Ab initio vertical excitation spectra of ${\mathrm{CH}}_3\mathrm{I}$ and ${\mathrm{CF}}_3\mathrm{I}$ are in agreement with the experimental observation. The curve crossing region is around 2.371 Å for ${\mathrm{CH}}_3\mathrm{I}$ and ${\mathrm{CF}}_3\mathrm{I}.$ The potential curves of the repulsive excited states have larger slope for ${\mathrm{CF}}_3\mathrm{I},$ suggesting a higher velocity and decreased intersystem crossing probability on fluorination. We also report the potential curves and the region of curve crossing for ${\mathrm{CH}}_3\mathrm{Br}$ and ${\mathrm{CH}}_3\mathrm{Cl}.$