Crystalline silica (SiO2) is a major material used in many technologies, yet the exact surface structures of silica polymorphs are still mostly unknown. Here we perform a comprehensive study of surface reconstructions of α-cristobalite (001), α-quartz (001) and stishovite (110) and (100) using evolutionary algorithm USPEX in conjunction with ab initio calculations. We found the well-known “dense surface” to be among low-energy reconstructions of α-quartz (001), as well as its previously proposed distorted version, which we call “shifted surface”. For cristobalite and stishovite we show the formation of reconstructions without dangling bonds which share common features with well-known “dense surface” of α-quartz (001). We call them “dense cristobalite” and “dense stishovite” – all of these have honeycomb arrangements of corner-sharing SiO4-tetrahedra in the surface layers. These tetrahedral honeycombs have very low surface energies, and such tetrahedral surface pattern is observed even in stishovite (the bulk structure of which has SiO6-octahedra, rather than SiO4-tetrahedra).

In this paper, we employ state-of-the-art theoretical approaches to elucidate the structures of the (011) surface of rutile (R-)TiO2. An unexpectedly rich chemistry has been uncovered. Titanyl-TiO2 and titanyl-Ti2O3 reconstructions can be used for rationalizing the experimental findings, matching the STM images and the changes in the band gap. From the viewpoint of thermodynamics, the predicted MF(111)-TiO reconstruction is more reasonable than the previously proposed MF(111)-TiO3 model, although there is a structural similarity. The richness of surface phases, the formation of which is driven by thermodynamic conditions and surface stress release, implies the multifunctionality of the R-TiO2(011) surface. After the clarification of TiO2(011) and TiO2(110) surface structures {PRL, 2014, 113, 266101} (the most important surfaces of rutile), the origin of the Brønsted acidity of R-TiO2, which has remained a mystery at the atomic level, can also be addressed in the near future.

A simple understanding on the trend of stability for transition metal carbides.

Oxidation of silicon nanoclusters depending on the temperature and oxygen pressure is explored from first principles using the evolutionary algorithm, and structural and thermodynamic analysis. From our calculations of 90 SiO clusters we found that under normal conditions oxidation does not stop at the stoichiometric SiO composition, as it does in bulk silicon, but goes further placing extra oxygen atoms on the cluster surface. These extra atoms are responsible for light emission, relevant to reactive oxygen species and many of them are magnetic. We argue that the super-oxidation effect is size-independent and discuss its relevance to nanotechnology and miscellaneous applications, including biomedical ones.

Fermi surfaces are essential for predicting, characterizing and controlling the properties of crystalline metals and semiconductors. Angle-resolved photoemission spectroscopy (ARPES) is the only technique directly probing the Fermi surface by measuring the Fermi momenta (kF) from energy- and angular distribution of photoelectrons dislodged by monochromatic light. Existing apparatus is able to determine a number of kF -vectors simultaneously, but direct high-resolution 3D Fermi surface mapping remains problematic. As a result, no such datasets exist, strongly limiting our knowledge about the Fermi surfaces. Here we show that using a simpler instrumentation it is possible to perform 3D-mapping within a very short time interval and with very high resolution. We present the first detailed experimental 3D Fermi surface as well as other experimental results featuring advantages of our technique. In combination with various light sources our methodology and instrumentation offer new opportunities for high-resolution ARPES in the physical and life sciences.