Serial femtosecond crystallography requires reliable and efficient delivery of fresh crystals across the beam of an X-ray free-electron laser over the course of an experiment. We introduce a double-flow focusing nozzle to meet this challenge, with significantly reduced sample consumption, while improving jet stability over previous generations of nozzles. We demonstrate its use to determine the first room-temperature structure of RNA polymerase II at high resolution, revealing new structural details. Moreover, the double flow-focusing nozzles were successfully tested with three other protein samples and the first room temperature structure of an extradiol ring-cleaving dioxygenase was solved by utilizing the improved operation and characteristics of these devices.
Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a well-characterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 μm diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 Ångström were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here.
Although several different approaches have been proposed for the calculation of the band structure, the empirical methods have proven to be more convenient, since we can arrive at a reasonable result close to what has been found experimentally without a huge computational trade-off by varying some relevant parameters. Moreover, a method based on a plane wave basis has been found to be extremely compatible with advanced methods for device modeling and simulation such as a semi-classical Monte Carlo. The purpose of this study is to extract fitting parameters for the calculation of band structure of graphene using the empirical pseudopotential method, which can be used for further research, such as theoretical modeling and simulation of graphene-based devices. Since various methods have been proposed for the calculation of these pseudopotentials, we will also briefly study the effect of different pseudopotentials on the band structure of bilayer graphene.