We reproduce the experimentally observed polymorph stability of the tetramorph pyrazinamide using periodic density functional theory (DFT) calculations augmented with an empirical dispersion term. This was only possible using highly accurate experimental structures, including a model of a disordered polymorph. Further, we demonstrate that a large basis set and very tight integration criteria are needed in the calculations. This study highlights some of the present challenges in crystal structure prediction methods: to obtain sufficiently accurate trial structures and to take into account the possibility of crystal disorder.

The SOLARIS synchrotron located in Krakow, Poland, is a third-generation light source operating at medium electron energy. The first synchrotron light was observed in 2015, and the consequent development of infrastructure lead to the first users’ experiments at soft X-ray energies in 2018. Presently, SOLARIS expands its operation towards hard X-rays with continuous developments of the beamlines and concurrent infrastructure. In the following, we will summarize the SOLARIS synchrotron design, and describe the beamlines and research infrastructure together with the main performance parameters, upgrade, and development plans.

Two-dimensional electron gases (2DEGs) at surfaces and interfaces of semiconductors are described straightforwardly with a one-dimensional (1D) self-consistent Poisson-Schrödinger scheme. However, their band energies have not been modeled correctly in this way. Using angle-resolved photoelectron spectroscopy we study the band structures of 2DEGs formed at sulfur-passivated surfaces of InAs(001) as a model system. Electronic properties of these surfaces are tuned by changing the S coverage, while keeping a high-quality interface, free of defects and with a constant doping density. In contrast to earlier studies we show that the Poisson-Schrödinger scheme predicts the 2DEG band energies correctly but it is indispensable to take into account the existence of the physical surface. The surface substantially influences the band energies beyond simple electrostatics, by setting nontrivial boundary conditions for 2DEG wave functions.

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We have performed a study of thermal graphitization of SiC (0001) surface in the high-purity molecular beam of Si atoms obtained from a controllable source. With the aid of Si beam, we have been able to achieve the semi-equilibrium reaction conditions and to control the growth rate of graphene film freely until complete stop of the graphitization, at the test temperature of 1350 °C. Samples treated in Si beam are characterized by larger and homogeneous areas of graphene having uniform thickness, and much improved crystallographic ordering. This is attributed mainly to the improved buffer layer structure. The buffer layer shows neither disordered regions, nor point defects, which are prevalent in UHV-annealed samples. Significantly smaller concentrations of other surface defects are also observed. The used approach is a promising alternative to more commonly used buffer gas graphitization methods. Apart from the precise control for process parameters and very high process purity, it also allows for a co-deposition of other atoms at the growth stage.