Vladimir S Bystrov has completed PhD, Dr. Habil.Phys. Dr.Sci. Phys. & Math. from Russian Academy of Sciences. Since 1993, he has his expertise in various fields of computational molecular modeling, computational exploration and computer simulation of nonlinear multifunctional nanomaterials and different organic & bio-molecular nano-structures such as: bioferroelectric & polymer PVDF/PVDF-TrFE thin ferroelectric films, graphene/oxide graphene and related polar composite nanomaterials; amino acids (glycine, etc.), peptides nanotubes, thymine & DNA; hydroxyapatite (HAP) & nanoparticles, etc. Computational studies of nanostructures were made using the molecular mechanics, quantum-chemical calculations (ab initio, DFT, semi-empirical methods), molecular dynamics (MD) on the base of various software (HyperChem, AIMPRO, VASP, etc.) and clusters in Russia IMPB & KIAM, Linux cluster in University of Aveiro, Portugal. He is a Head of the Group for Computer Modelling of Nanostructures and Biosystems of IMPB-KIAM RAS, Pushchino.
A new model of the structure of hydroxyapatite (HAP) with defects of the oxygen vacancy type and hydroxyl group vacancy type has been developed. The model made it possible to explain the change in the optical properties of the HAP and provide for the mechanism of its photocatalytic activity. The obtained new results and knowledge allow us to already purposefully change the optical properties of HAP (introduction of the necessary type of the defects) and control the photocatalytic activity of HAP, which is extremely important for many practical applications (in the cleaning the environment, including the water from harmful impurities and components, in the chemical photocatalytic synthesis, in the antimicrobial treatment, etc.). The model is developed on the basis of several new approaches to the density functional theory (DFT) with combined application of the various hybrid and exchange-correlation functionals, and also taking into account the Coulomb shielding of the defect charge, which allows made more exact and accurate calculation of structural, optical and other properties of HAP materials. These approaches continue to develop on some new more complex models of the super-cells of HAP, which will allow us to obtain a number of even more highly accurate results of calculations of the HAP properties for both pure and with different defects. The computed properties of HAP material with super-cell model (2x2x2 - 8 unit cell) are considered using semi-local (PBE potential) and hybrid exchange-correlation functionals with different fraction of exact exchange contribution. The excitation properties are compared with the results of GW-approximation method for calculation of quasi-particle band structure. It was shown that optical properties of bulk HAP are best described using B3LYP exchange-correlation functional and for pure HAP have band gap Eg ~ 7.3 eV, while with O vacancy it is lowered.
Michał Stępień graduated MSc from the AGH University of Science and Technology in 2010. He received his PhD degree in 2015 (Synthesis of oxides nanostructures on the surface of selected transition metals) under the guidance of Professor Krzysztof Fitzner. His research interests are based on synthesis and surface modification oxides nanotubes. Now he is a Research Worker in AGH in Department of Physical Chemistry and Metallurgy of Non-Ferrous Metals.
Depending on the thickness of the oxide layer on niobium different properties of this material can be obtained, which can be exploited in sensing, decorative materials, electronic paper and displays. The aim of this work is to produce the oxide layer in the controlled way utilizing electrochemical experiment. The layer of the oxide will be formed by anodization of Nb electrode in acidic aqueous solution. Then, the electrochemical impedance spectrometry (EIS) is used to control the thickness of the growing layer due to the relation: where: ε0 – permittivity of the vacuum; εr – permittivity of the oxide film; A – geometric area of the oxide; d – barrier oxide thickness; C – capacitance obtained from EIS after proper choice of the equivalent circuit. However, successful control requires exact knowledge of dielectric constant of niobium oxide. Depending on oxidation conditions, different values of εr can be obtained. Therefore, this value will be verified by using simultaneously EIS and ellipsometric measurements.