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A molecular dynamics simulation of the self-diffusion of thorium cations in ThO2 nanocrystals with a free surface is conducted. It is shown that a vacancy in the bulk of a crystal initiates a complex collective movement of cations, in which the interstitial positions surrounding the vacancy are involved. The diffusion coefficients of cations in the temperature range are calculated. The effective activation energy of diffusion is ED = (7.6 ± 0.7) eV. [ABSTRACT FROM AUTHOR]

A molecular dynamics simulation of sintering of two octahedral uranium dioxide nanocrystals contacting in the vertex region is carried out. Two main stages of the sintering process are observed. At the beginning of the simulation, the neck between the crystallites is formed due to the mutual attraction of the adjacent (111) faces. Further increase in the neck thickness occurs due to transport of the material from the surface of the crystallites in a much slower diffusion process. The estimate of the activation energy of this process is in the range from 11 to 14 eV. [ABSTRACT FROM AUTHOR]

Atomistic understanding of the interaction between defects and active surface of the sensor is necessary for the developing devices detecting bio-and gas mixtures. We performed first principles computer simulations of the carbon dioxide (CO2) molecule adsorption on a ZnO surface in various configurations and location on the surface. It is shown that the tridentate configuration is the most energetically favorable, the binding energy of the molecule weakly depends on the surface coverage. The presence of intrinsic defects on the surface, such as an oxygen vacancy, leads to a small reduction of the binding energy. The observed data from the NEXAFS experiment and hypothetical formation of a new compound H2CO on the surface are discussed in the light of our calculations. [ABSTRACT FROM AUTHOR]

The process of mass transfer in (U,Pu)O2 nanocrystals is studied using the molecular dynamics simulation. The dependence of the vacancy concentration on temperature was estimated by calculating the time of presence of the vacancies in the crystallite bulk. The effective formation energy of vacancies obtained from this dependence was (10 ± 2) eV. Within the limits of error, this energy coincides with the formation energy of the Schottky defect calculated by the lattice static method, and also with the effective energy characterizing the frequency of vacancy formation. [ABSTRACT FROM AUTHOR]