A Study of Evaporation of Complex Oxide Systems Based on Chromium(III) Oxide

Evaporation of chromium ore and concentrates was studied using high-temperature differential mass-spectrometry. The data obtained, concerning the component vapor pressures in evaporation of complex oxide systems in the range 1700-2100 K, can be used to calculate the evaporation loss in melting and to assess the possibility of utilization of the sublimates formed.     

Ab initio study of exciton transfer dynamics from a core–shell semiconductor quantum dot to a porphyrin-sensitizer

The observed resonance energy transfer in nanoassemblies of CdSe/ZnS quantum dots and pyridyl-substituted free-base porphyrin molecules [Zenkevich et al., J. Phys. Chem. B 109 (2005) 8679] is studied computationally by ab initio electronic structure and quantum dynamics approaches. The system harvests light in a broad energy range and can transfer the excitation from the dot through the porphyrin to oxygen, generating singlet oxygen for medical applications. The geometric structure, electronic energies, and transition dipole moments are derived by density functional theory and are utilized for calculating the Förster coupling between the excitons residing on the quantum dot and the porphyrin. The direction and rate of the irreversible exciton transfer is determined by the initial photoexcitation of the dot, the dot–porphyrin coupling and the interaction to the electronic subsystem with the vibrational environment. The simulated electronic structure and dynamics are in good agreement with the experimental data and provide real-time atomistic details of the energy transfer mechanism.     

Parallel implementation of γ‐point pseudopotential plane‐wave DFT with exact exchange

Semi‐local functionals commonly used in density functional theory (DFT) studies of solids usually fail to reproduce localized states such as trapped holes, polarons, excitons, and solitons. This failure is ascribed to self‐interaction which creates a Coulomb barrier to localization. Pragmatic approaches in which the exchange correlation functionals are augmented with small amount of exact exchange (hybrid‐DFT, e.g., B3LYP and PBE0) have shown to promise in rectifying this type of failure, as well as producing more accurate band gaps and reaction barriers. The evaluation of exact exchange is challenging for large, solid state systems with periodic boundary conditions, especially when plane‐wave basis sets are used. We have developed parallel algorithms for implementing exact exchange into pseudopotential plane‐wave DFT program and we have implemented them in the NWChem program package. The technique developed can readily be employed in Γ‐point plane‐wave DFT programs. Furthermore, atomic forces and stresses are straightforward to implement, making it applicable to both confined and extended systems, as well as to Car‐Parrinello ab initio molecular dynamic simulations. This method has been applied to several systems for which conventional DFT methods do not work well, including calculations for band gaps in oxides and the electronic structure of a charge trapped state in the Fe(II) containing mica, annite. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Catalytic conversion of COS and CS2 under an excess of sulfur dioxide

Conversion of organosulfur components (COS and CS₂) in catalytic processing of a real reduced sulfurous gas was experimentally studied.     

Electron density redistribution accounts for half the cooperativity of alpha helix formation

The energy of alpha helix formation is well known to be highly cooperative, but the origin and relative importance of the contributions to helical cooperativity have been unclear. Here we separate the energy of helix formation into short range and long range components by using two series of helical dimers of variable length. In one dimer series two monomeric helices interact by forming hydrogen bonds, while in the other they are coupled only through long range, primarily electrostatic interactions. Using Density Functional Theory, we find that approximately half of the cooperativity of helix formation is due to electrostatic interactions between residues, while the other half is due to nonadditive many-body effects brought about by redistribution of electron density with helix length.     

Influence of SiO2 on the Equilibrium in the Cu-Ni-Cu2O-NiO System

The equilibrium between a copper-nickel alloy and an oxide melt in the Cu₂O-NiO-SiO₂ system was studied experimentally. The distribution coefficients of nickel were determined as a function of the content of silicon dioxide, and the ratio of activity coefficients of nickel and copper oxides at 1300°C was found.     

Determining the Activity Coefficients of Copper and Nickel Oxides in Melts of the System Cu2O-NiO

Equilibria between a copper-nickel alloy and oxide melt of the binary system Cu₂O-NiO were studied and the activity coefficients of copper and nickel oxides at 1573 K in the homogeneity region of the oxide melt (up to 11.6 mol % NiO) were determined. Similar values were also found by calculation from the phase diagram of Cu₂O-NiO.     

Solubility of Carbon in Sulfide Melts of the System Fe-Ni-S

The solubility of carbon in iron-nickel sulfide melts at 1673 K was studied in the entire range of compositions of the Fe-FeS-Ni₃S₂-Ni tetragon. The boundaries of the stratification area were determined in this system upon its being saturated with carbon. Lines of carbon isosolubility are plotted in the tetragon field outside the stratification area.     

Distribution of Copper,Nickel, Cobalt and Iron between Products of Smelting of Copper Concentrate Obtained by Flotation of Converter Matte

An experimental study of the equilibrium between the bottom phase (sulfide melt or copper) and slag in neutral and oxidizing atmospheres yielded dependences of the content of dissolved copper, nickel, and cobalt in the slag on that of sulfur in the sulfide melt and also the dependence of the content of dissolved copper and nickel on that of nickel in the metallic melt. The distribution coefficients of the metals between copper and slag were determined and compared with the results of other investigations.