Theoretical calculations of hydrogen adsorption by SnO2 (110) surface: Effect of doping and calcination

A pseudopotential plane-wave based density functional theory simulations of the hydrogen adsorption on rutile SnO2 (110) surface is reported. It is found that on doping with trivalent indium, the surface becomes unstable due to the formation of bridging oxygen vacancies. At sufficiently low doping level, the surface stabilizes at an oxygen vacancy to indium ratio of 1:2. Our calculations predict that at a higher doping level of 9 at. %, this ratio becomes larger, and point out a way to synthesize p-type conducting SnO2 thin films. The binding energy of SnO2 (110) surface with adsorbed hydrogen atoms display a maximum at 3-6 at. % of indium doping. This is in good agreement with the experimental results obtained from the SnO2-based hydrogen sensor\u27s sensitivity measurements given by Drake et al. [J. Appl. Phys. 101, 104307 (2007)]. The theoretical modeling explains that the calcinations treatment can critically affect the sensitivity of the hydrogen sensor due to the enhancement of the binding energy between the SnO2 surface and the adsorbed hydrogen atoms

Oxygen evolution reaction on a N-doped Co0.5-terminated Co3O4 (001) surface

The project AP05131211 “First principles investigation on catalytic properties of N-doped Co3O4.” was funded by the Ministry of Education and Science of the Republic of Kazakhstan. The work was partly supported by COST (European Cooperation in science and Technology) Action 18234 (YM and EK). The work of T. Inerbaev was performed under the state assignment of Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences. YM and EK thank Sun-to-Chem project of ERA Net.Recent experimental findings suggest that the catalytic activity of Co3O4 for oxygen evolution reaction (OER) could be improved by nitrogen doping. We present preliminary OER modelling on a N-doped Co3O4 surface, with varying concentration of the dopant and its spatial distribution around Cooct and Cotet adsorption sites. The overpotential was calculated for two adsorption sites on seven types of N-doped Co3O4 surface. The largest calculated overpotential value for a N-doped surface was ~1V. This work is licensed under a CC BY 4.0 license.Ministry of Education and Science of the Republic of Kazakhstan, project AP0513121; COST Action 18234; Sobolev Institute of Geology and Mineralogy Siberian Branch of the Russian Academy of Sciences; Sun-to-Chem project of ERA Net; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Quantum chemistry of quantum dots: Effects of ligands and oxidation

We report Gaussian basis set density functional theory (DFT) calculations of the structure and spectra of several colloidal quantum dots (QDs) with a (CdSe)(n) core (n=6,15,17), that are either passivated by trimethylphosphine oxide ligands, or unpassivated and oxidized. From the ground state geometry optimization results we conclude that trimethylphosphine oxide ligands preserve the wurtzite structure of the QDs. Evaporation of the ligands may lead to surface reconstruction. We found that the number of two-coordinated atoms on the nanoparticle\u27s surface is the critical parameter defining the optical absorption properties. For (CdSe)(15) wurtzite-derived QD this number is maximal among all considered QDs and the optical absorption spectrum is strongly redshifted compared to QDs with threefold coordinated surface atoms. According to the time-dependent DFT results, surface reconstruction is accompanied by a significant decrease in the linear absorption. Oxidation of QDs destroys the perfection of the QD surface, increases the number of two-coordinated atoms and results in the appearance of an infrared absorption peak close to 700 nm. The vacant orbitals responsible for this near infrared transition have strong Se-O antibonding character. Conclusions of this study may be used in optimization of engineered nanoparticles for photodetectors and photovoltaic devices

Density Functional Study Of Oxygen Vacancy Formation And Spin Density Distribution In Octahedral Ceria Nanoparticles

We report plane wave basis density functional theory (DFT) calculations of the oxygen vacancies formation energy in nanocrystalline CeO2-× in comparison with corresponding results for bulk and (111) CeO2 surface. Effects of strong electronic correlation of Ce4f states are taken into account through the use of an effective on-site Coulomb repulsive interaction within DFT+U approach. Different combinations of exchange-correlation functionals and corresponding U values reported in the literature are tested and the obtained results compared with experimental data. We found that both absolute values and trends in oxygen vacancy formation energy depend on the value of U and associated with degree of localization of Ce4f states. Effect of oxygen vacancy and geometry optimization method on spatial spin distribution in model ceria nanoparticles is also discussed. © Springer-Verlag 2010

Reducible And Non-Reducible Defect Clusters In Tin-Doped Indium Oxide

Density functional theory calculations are used to estimate the energy of interstitial oxygen (Oi) released from tin-doped indium oxide (ITO). The currently accepted explanation of defect clusters\u27 irreducibility is based on different arrangements of doping atoms around Oi. In the present contribution we demonstrate that this concept has only a limited domain of applicability and explains the relative stability of different defect clusters with the same and fixed Sn:Oi ratio. To describe practically the important case of ITO treatment under strong reduction conditions another limiting case of varying Sn:Oi ratio is considered. It is found that in this particular case local coordination of doping atoms around Oi plays only a minor role. The relative stability of the oxidized defect clusters has caused a noticeable change in the electronic part of the defect formation energy, i.e. the chemical potential of the conduction electrons determines the equilibrium concentration of the interstitial oxygen atoms. © 2009 Elsevier Ltd. All rights reserved

Tuning Hydrated Nanoceria Surfaces: Experimental/Theoretical Investigations Of Ion Exchange And Implications In Organic And Inorganic Interactions

Long-term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized, and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time-dependent zeta (ζ) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature, and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H+) and the neighboring hydroxyls ions (OH-). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H+ ions on the CNP surface is kinetically more favorable while the adsorption of OH- ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical. © 2010 American Chemical Society

Spin Unrestricted Excited State Relaxation Study of Vanadium(IV)-Doped Anatase

Atomistic modeling of light driven electron dynamics are important in studies of photoactive materials. Spin-resolved electronic structure calculations become necessary when dealing with transition metal, magnetic, and even some carbon materials, intermediates, and radicals. An approximate treatment can be pursued in the basis of spin-collinear density functional theory. Most transition-metal compounds exhibit open shell nonsinglet configurations, necessitating special treatment of electrons with α/β spin projections. By separate treatment of electronic states with the α/β spin components one is able to describe a broader range of materials, identify new channels of relaxation and charge transfer, and provide knowledge for rational design of new materials in solar energy harvesting and information storage. For this methodology, named <i>spin-resolved electron dynamics</i>, spin-polarized DFT is used as the basis to implement nonadiabatic molecular dynamics. At ambient temperatures, the thermal lattice vibrations results in orbital and energy fluctuations with time. Nonadiabatic couplings are then calculated, which control the dissipative dynamics of the spin resolved density matrix. Different initial excitations are then analyzed and used to calculate relaxation dynamics. <i>Spin-resolved electronic dynamics</i> approach (SREDA) is applied to study vanadium­(IV) substitutionally doped bulk anatase in a doublet ground state. The results show that a difference in the electronic structure for α and β spin components determines consequences in optical excitations and electronic dynamics pathways experienced by electrons with α and β spin projections. Specifically, the lone occupied V 3d α-orbital increases the range of absorption and defines the rates and pathways of relaxation for both holes and electrons with α-spin projection. Optical excitations involving occupied V 3d α-orbital are responsible for IR-range absorption, followed by nonradiative relaxation. Certain transitions involving orbitals of α-spin component occur in the visible range and induce localization of a negative charge on the V ion for an extended time period. The slower nonradiative relaxation rate of α-excitations is rationally explained as a consequence of difference of electronic structure for α and β spin projections and specific pattern of energy levels contributed by doping. Specifically, excitations involving orbitals with α-projection of spin experience transitions through larger subgaps in the conduction band compared to the ones experienced by similar excitations involving orbitals with β-projection of spin. It is anticipated that this methodology can be broadly implemented on multiple applications of transition metal based materials, including optoelectronics, information storage, laser crystals, dyes, photovoltaic materials, and metal oxides for photoelectrochemical water splitting