Vibrational properties of nanoparticles iron oxide by Raman spectroscopy

The crystal structure and atomic dynamics of Fe3O4 nanoparticles have been studied. The crystal structure of iron oxide nanoparticles was determined by X-ray diffraction. The analysis showed that the crystal structure of [Formula: see text] 50–100 nm dimensional iron oxide corresponds to a high symmetry cubic crystal structure. Calculations have shown that there are four infrared active, five Raman active and seven hyper-Raman active modes in the space group Fd-3m with cubic symmetry. Four of these modes have been observed using Raman spectroscopy: 213, 271, 380 and 591 cm[Formula: see text]. The vibrational modes are interpreted by Gaussian function. It was found that these vibration modes correspond to the vibration of O–Fe–O bonds and iron-oxygen polyhedra.

NMR Crystallography at Fast Magic-Angle Spinning Frequencies: Application of Novel Recoupling Methods

Chemical characterisation of active pharmaceutical compounds can be challenging, especially when these molecules exhibit tautomeric or desmotropic behaviour. The complexity can increase manyfold if these molecules are not susceptible to crystallisation. Solid-state NMR has been employed effectively for characterising such molecules. However, characterisation of a molecule is just a first step in identifying the differences in the crystalline structure. 1 H solid-state Nuclear Magnetic Resonance (ssNMR) studies on these molecules at fast magic-angle-spinning frequencies can provide a wealth of information and may be used along with ab initio calculations to predict the crystal structure in the absence of X-ray crystallographic studies. In this work, we attempted to use solid-state NMR to measure 1 H - 1 H distances that can be used as restraints for crystal structure calculations. We performed studies on the desmotropic forms of albendazole.

Modelling of Atomic Imaging and Evaporation in the Field Ion Microscope

Imaging and evaporation of atoms in the field ion microscope (FIM) has been modelled by using finite difference methods to calculate the voltage distribution around a tip and hence the electric field strength experienced by individual atoms. Atoms are evaporated based on field strength using a number of different mathematical models which yield broadly similar results. The tip shapes and simulated FIM images produced show strong agreement with experimental results for tips of the same orientation and crystal structure. Calculations have also been made to estimate the effects on resolution of using a field-sharpened tip for scanning probe microscopy.

Embedded Cluster Model: Application to Molecular Crystals

ABSTRACTMultiscale modeling using an embedded cluster approach is presented and applied to study the structure and properties of molecular crystals. We discuss the results of hydrostatic compression modeling of 1,1-diamino-2,2-dinitroethylene obtained with the embedded cluster model and the Hartree-Fock method and compare these with the full periodic crystal structure calculations. Details of the electronic structure of the perfect, highly compressed material are discussed. The results demonstrate the applicability of the embedded cluster model. We show that the band gap of the perfect material is not sensitive to hydrostatic compression, but some changes induced by the pressure take place in the valence band.