Research experience

A computer simulation study of the reactivity of nitroxides

Nitroxides have been recently recognized as an important, new class of antioxidants. Several computational methods have been previously employed in order to predict the redox potentials of nitroxyl radicals and to better understanding of the catalytic cycle, antioxidant and/or scavenging potency of different nitroxides derivatives. In this work, the redox behavior of a series of nitroxyl radicals was analyzed in parallel with computational studies to extend our knowledge of the structural features necessary for anticipating the nitroxides scavenging abilities against ROS (reactive oxygen species). Quantum chemical calculations on some typical nitroxyl radicals and corresponding oxo-ammonium cations were performed at the unrestricted level of hybrid density functional theory. Nitroxide oxidation via ROS to the cation was treated as adiabatic reaction and both the starting structure and the oxidized one were fully optimized using the 6-31+G* basis set. Electron and spin densities, electrostatic potentials and thermodynamic properties were obtained from single point calculations using 6-311+G* basis set. Similar calculations were performed for hydrated molecules: solvent effects were evaluated by the polarizable continuum model.

Excess electron localization in concentrated ionic solutions. A computer simulation research

The calculations were split into three stages: a) Classical Molecular Dynamics simulation of the aqueous solutions structure, b) Quantum Molecular Dynamics of the excess electron localization in the solutions and c) Quantum Mechanical simulations of the excess electron absorption spectrum. Molecular Dynamics simulations of LiCl, NaCl, MgCl₂ and NaOH aqueous solutions were performed with the flexible model of water molecule. Thanks to the analysis of the structural and dynamical properties of the solutions, the regions of the crystalline-order at high concentrations have been found. The subsets originating from equilibrated solutions were selected to perform Quantum Car-Parinello Molecular Dynamics of the excess electron localization. The calculations were performed on the DFT level using plane wave basis set, Goedecker-type pseudopotentials and LSD approximation. Obtained electron spin densities were analyzed using pair correlation functions. Clusters composed of the localized electron and its surrounding were selected to calculate the absorption spectrum with time-dependent, non-local DFT method. Three electron-trapping sites have been found in aqueous ionic solutions: purely water environment (responsible for e_vis absorption band), cationic traps (responsible for e_ir band) and occasionally, traps of the “F‑centre” type.

Committee for Scientific Research (KBN) grant nr: KBN 3T09A 06617

Structure and catalytic power of transition metals and their alloys

The constant pressure Molecular Dynamics simulations of the neat metals Ni, Cu, Ag, Pd, Au, Pt and the alloys Ni_xCu_y, Ag_xPd_y, Au_xPt_y were performed. Geometrical structures of possible catalytic centres of an alloy were analysed with RDFs and stochastic geometry methods. The non-local DFT calculations of energy of the hydrogen adsorption on the alloys were performed to measure the catalytic power of a given alloy for the H₂ dissociation reaction. It was found that the highest value of the catalytic power is exhibited by Ni_xCu_1-x alloys with x between 0.3 and 0.6 and some Au_xPt_l-x alloys and the neat metals Ni and Pt.

Structure of the water and aqueous solutions in 16-300K. Spectroscopic, radiation and computer simulation investigations

The structure of aqueous solutions of simple ionic salts in the region of very high concentrations was studied using the classical Molecular Dynamics method. The structures of hydration shells of the ions and the topological properties of the ionic structures were analysed using such tools as radial distribution functions, Voronoi tessellations, O'Keeffe coordination numbers, etc. Ruff's theory of ionic quasi-lattices in concentrated solutions was investigated for LiCl, NaCl, NaOH and MgCl₂ solutions. For a wide range of concentrations, from 6 M to 19 M, the postulated presence of the multi-ion structures has been established. The radial distribution functions as well as the distributions of the non-sphericity factor of the Voronoi polyhedra undoubtedly support the lattice theory of concentrated electrolytes, providing proofs for existence of the ordered ionic structures in the solutions.

Committee for Scientific Research (KBN) grant nr: KBN 3T09A 2917