The WIEN2k program is based on the augmented plane wave plus local orbitals (APW+lo) method to solve the Kohn–Sham equations of density functional theory. The APW+lo method, which considers all electrons (core and valence) self-consistently in a full-potential treatment, is implemented very efficiently in WIEN2k, since various types of parallelization are available and many optimized numerical libraries can be used. Many properties can be calculated, ranging from the basic ones, such as the electronic band structure or the optimized atomic structure, to more specialized ones such as the nuclear magnetic resonance shielding tensor or the electric polarization. After a brief presentation of the APW+lo method, we review the usage, capabilities, and features of WIEN2k (version 19) in detail. The various options, properties, and available approximations for the exchange-correlation functional, as well as the external libraries or programs that can be used with WIEN2k, are mentioned. References to relevant applications and some examples are also given.

Aspects of the progress over the last 40–50 years in calculating the electronic structure of solids and surfaces are sketched in the context of collaboration on the code now called WIEN2k. Different facets that are relevant for material sciences are discussed, ranging from quantum mechanics to the augmented plane wave (APW) method, as well as improvements in computer hardware and algorithms and related numerical accuracy. In this long period, the complexity and realism of applications to condensed matter systems has significantly increased and many properties which are closely related to experiments can now be calculated. This progress is illustrated by the fact that WIEN2k now is used worldwide by more than 1600 groups. The major steps in this development are illustrated for a few selected examples.

Crystallography and quantum mechanics have always been tightly connected because reliable quantum mechanical models are needed to determine crystal structures. Due to this natural synergy, nowadays accurate distributions of electrons in space can be obtained from diffraction and scattering experiments. In the original definition of quantum crystallography (QCr) given by Massa, Karle and Huang, direct extraction of wavefunctions or density matrices from measured intensities of reflections or, conversely, ad hoc quantum mechanical calculations to enhance the accuracy of the crystallographic refinement are implicated. Nevertheless, many other active and emerging research areas involving quantum mechanics and scattering experiments are not covered by the original definition although they enable to observe and explain quantum phenomena as accurately and successfully as the original strategies. Therefore, we give an overview over current research that is related to a broader notion of QCr, and discuss options how QCr can evolve to become a complete and independent domain of natural sciences. The goal of this paper is to initiate discussions around QCr, but not to find a final definition of the field.

Several recent studies have shown that SCAN, a functional belonging to the meta-generalized gradient approximation (MGGA) family, leads to significantly overestimated magnetic moments in itinerant ferromagnetic metals. However, this behavior is not inherent to the MGGA level of approximation since TPSS, for instance, does not lead to such severe overestimations. In order to provide a broader view of the accuracy of MGGA functionals for magnetism, we extend the assessment to more functionals but also to antiferromagnetic solids. The results show that to describe magnetism there is overall no real advantage in using a MGGA functional compared to GGAs. For both types of approximation, an improvement in ferromagnetic metals is necessarily accompanied by a deterioration (underestimation) in antiferromagnetic insulators, and vice versa. We also provide some analysis in order to understand in more detail the relation between the mathematical form of the functionals and the results.

The dynamics of carboxylate ligands on the surface of zirconium oxo clusters was investigated in two case studies. Zr₄O₂(methacrylate)₁₂ was investigated by one- and two dimensional NMR spectra both in the solid state and in solution. In solution, the cluster is C_2h symmetric; stepwise intramolecular exchange of the four non-equivalent ligands was observed when the temperature was raised from −80 °C to −50 °C. The individual exchange processes were assigned to different ligand positions. Ab initio molecular dynamics simulations were performed for Zr₆(OH)₄O₄(formate)₁₂ to study the trajectory for the rearrangement of three chelating ligands into bridging positions, i.e. the conversion of the C₃-symmetric into an O_h-symmetric cluster. The observation of a dip in the energy barrier along the reaction coordinate was related to the intermediate formation of hydrogen bonds between the moving oxygen atom of the rearranging ligand and a μ₃-OH group of the cluster. Thus, the motion of the ligand requires a concerted motion in three dimensions.

Solid electrolytes play an important role in several technological applications, such as fuel cells. Optimization of such materials is often done by trial and error. The work of Andersson et al . (1) in this issue of PNAS demonstrates that the choice of dopants can be guided by computer simulations, in which parameters that are essential for the high ionic conductivity are determined from a series of first-principles density functional theory (DFT) calculations (2). The material of interest is ceria (CeO2), which can be doped to optimize the ionic conductivity. The parent compound has a simple cubic structure (Fig. 1), in which the Ce ions form a face-centered-cubic (fcc) structure and the oxygen ions form a simple cubic sublattice. The current flows by means of oxygen ions, which are transported through the lattice in a vacancy-assisted activated process. Vacancies occur, for example, when ceria is … *E-mail: kschwarz{at}theochem.tuwien.ac.at