Aleksandar Staykov

The direct synthesis of hydrogen peroxide on Pd and Pd/Au catalysts was investigated with first-principle DFT methods for periodic two-dimensional surfaces. A two-step reaction mechanism was proposed starting from a superoxo precursor state of the dioxygen molecule on Pd surface and its subsequent reaction with two hydrogen atoms situated over neighboring 3-fold positions. A competitive reaction of dioxygen dissociation leading to the nonselective formation of water was found. We have shown that

The electrical rectifying properties of a single-molecule nanowire from the type donor−π-bridge−acceptor are investigated by means of the nonequilibrium Green's function method, combined with density functional theory (NEGF−DFT). The investigated nanowire is an oligo-1,4-phenylene ethylene with π-donor and π-acceptor groups attached on opposite sides of the molecule. The donor and acceptor wires are separated by a π-bridge, in contrast to the Aviram−Ratner rectifier, which is a donor−σ-bridge−ac

Density functional theory and low energy ion scattering spectroscopy were applied to study the mechanism of oxygen dissociation on the SrO-terminated surfaces of strontium titanate (SrTiO3) and iron-doped strontium titanate (SrTi1–xFexO3−δ). Our study reveals that while O2 dissociation is not favored on the SrO-terminated perovskite surface, oxygen vacancies can act as active sites and catalyze the O–O bond cleavage. Electron transfer from lattice oxygen atoms to the O2 molecule, mediated by the

A small addition of oxygen to hydrogen gas is known to mitigate the hydrogen embrittlement (HE) of steels. As atomic hydrogen dissolution in steels is responsible for embrittlement, catalysis of molecular hydrogen dissociation by the steel surface is an essential step in the embrittlement process. The most probable role of oxygen in mitigating HE is to inhibit the reactions between molecular hydrogen and the steel surface. To elucidate the mechanism of such surface reaction of hydrogen with the

A combined theoretical and experimental study was performed on diarylethenes and diarylethene-capped sexithiophenes aiming at an improved understanding of the electrochemical and photochemical ring-opening and ring-closing mechanisms. Theoretical calculations, based on DFT and TDDFT, suggested that the spatial distribution and the occupancy of the frontier orbitals determine and control the diarylethenes' ring-opening and ring-closing upon photoirradiation and electrochemical oxidation. Optimize

The optical photoswitching of conductivity of a diarylperfluorocyclopentene nanowire is investigated using Green's function method combined with density functional theory. A model closer to the real molecular electronic device is considered with relaxation of the molecular geometry under the interaction with external electric field. The ratio of conductance for the closed- and open-ring forms is on the order of magnitude 102. The influence of the HOMO−LUMO gaps and the spatial distributions of f

We investigated the competitive coadsorption of carbon monoxide and hydrogen gas on an iron surface with a 110 facet using density functional theory. Our study discusses the hydrogen dissociation reaction on a fresh iron surface and a surface with varying carbon monoxide coverage. Additionally, we investigated the carbon monoxide surface adsorption as a function of the carbon monoxide surface coverage. Our results show different trends for the carbon monoxide adsorption and hydrogen dissociation

Time dependent density functional theory (TDDFT) is used to study the important factors that control the photoisomerization of diarylperfluorocyclopentenes. The calculations are carried out for free molecules and for diarylperfluorocyclopentenes perturbed by gold atoms. Potential energy surfaces for the cyclization reaction are obtained for the ground state and for the excited states involved in the photoswitching. Analysis of the computed UV/vis spectra, the excitation energies, and the spatial

The structure, electronic properties, and catalytic activity toward oxygen activation of gold nanoclusters with size between 10 and 42 atoms were investigated with first principle methods. Nanoparticle symmetry, bond lengths, and surface charge distribution were analyzed and compared to those of macroscopic gold surfaces. Irregular charge distribution was found on the surfaces of nanoparticles consisting of fewer than 30 gold atoms. Nanoparticles with more than 30 atoms were characterized with c

Photoswitching of conductance through both stable isomers of salicylidene methylamine was investigated using nonequilibrium Green’s function method combined with density functional theory. This study demonstrates how the optically induced intramolecular proton transfer between the hydroxyl group and the amino group of salicylidene methylamine can lead to molecular size photodiode with on/off current ratio of 1 order of magnitude. It was further elucidated that the optical switching alone is not

The conductance through short DNA molecules connected to gold electrodes is studied with density functional theory and nonequilibrium Green’s function method combined with density functional theory. The anchoring of the molecules to the electrodes is investigated, and in addition to the covalent S−Au bond, weak interactions between the aromatic heterocyclic bases and the electrodes are found. These weak interactions are important for the electron transport through DNA molecules. A tunneling mech

The interaction of SrO terminated SrTiO₃ surface with molecular carbon dioxide and water has been investigated using first-principle theoretical methods and surface analysis techniques.

One to several nanometer-size nanoparticles possess supreme catalytic activity for a variety of important synthetic reactions compared to larger particles and bulk surfaces. However, a significant drawback is the catalyst durability as small, active nanoparticles tend to merge to form larger, less active nanocolloids. Tailoring the nanoparticle–surface support interaction could provide a means to limit nanoparticle mobility and thus prevent aggregation. In this study, we demonstrate the stabiliz

Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO₃ and iron doped SrTiO₃ were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO₃ and compared it to DOS of iron-doped SrTiO₃ with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.e. surface states, for both