We investigate the effect of acceptor-dopant cations on oxygen-vacancy migration in the perovskite oxide SrTiO3 by static lattice simulation techniques. We focus on two themes: dopant cations modifying the activation energies for vacancy migration, and dopant cations binding oxygen vacancies in binary associates. In both cases a variety of defect configurations exceeding the scope of first nearest neighbor (1NN) interaction is examined, i.e. 1NN, 2NN, 3NN, 4NN, and 5NN. The behavior of four divalent dopants (Ni2+, Fe2+, Co2+, and Mn2+) and one trivalent dopant (Al3+) is compared. The simulations predict that the binding energy of an oxygen vacancy to any of these dopants is negative at 1NN sites, but only converges to zero for 4NN sites. In addition the simulations show that the migration energy of a vacancy is affected by an acceptor-dopant cation over a length scale of several unit cells. A simple analytical model is used, together with the calculated site and activation energies, to predict how in general the ionic conductivity is affected by the interactions between oxygen vacancies and acceptor-dopant cations. The model predicts that the magnitude of these effects depends on the specific dopant, its concentration, and the temperature.

The migration of ions in HfO x was investigated by means of large-scale, classical molecular-dynamics simulations over the temperature range 1000 ≤ T/K ≤ 2000. Amorphous HfO x was studied in both stoichiometric and oxygen-deficient forms (i.e., with x = 2 and x = 1.9875); oxygen-deficient cubic and monoclinic phases were also studied. The mean square displacement of oxygen ions was found to evolve linearly as a function of time for the crystalline phases, as expected, but displayed significant negative deviations from linear behavior for the amorphous phases, that is, the behavior was sub-diffusive. That oxygen-ion migration was observed for the stoichiometric amorphous phase argues strongly against applying the traditional model of vacancy-mediated migration in crystals to amorphous HfO 2 . In addition, cation migration, whilst not observed for the crystalline phases (as no cation defects were present), was observed for both amorphous phases. In order to obtain activation enthalpies of migration, the residence times of the migrating ions were analyzed. The analysis reveals four activation enthalpies for the two amorphous phases: 0.29 eV, 0.46 eV, and 0.66 eV (values very close to those obtained for the monoclinic structure) plus a higher enthalpy of at least 0.85 eV. In comparison, the cubic phase is characterized by a single value of 0.43 eV. Simple kinetic Monte Carlo simulations suggest that the sub-diffusive behavior arises from nanoscale confinement of the migrating ions. Published by AIP Publishing. [http://dx

A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

The generation of anti-Frenkel pairs (oxygen vacancies and oxygen interstitials) in monoclinic and cubic HfO 2 under an applied electric field is examined. A thermodynamic model is used to derive an expression for the critical field strength required to generate an anti-Frenkel pair. The critical field strength of E cr aF ∼ 10 1 GVm −1 obtained for HfO 2 exceeds substantially the field strengths routinely employed in the forming and switching operations of resistive switching HfO 2 devices, suggesting that field-enhanced defect generation is negligible. Atomistic simulations with molecular static (MS) and molecular dynamic (MD) approaches support this finding. The MS calculations indicated a high formation energy of E aF ≈ 8 eV for the infinitely separated anti-Frenkel pair, and only a decrease to E aF ≈ 6 eV for the adjacent anti-Frenkel pair. The MD simulations showed no defect generation in either phase for E < 3 GVm −1 , and only sporadic defect generation in the monoclinic phase (at E = 3 GVm −1) with fast (t rec < 4 ps) recombination. At even higher E but below E cr aF both monoclinic and cubic structures became unstable as a result of field-induced deformation of the ionic potential wells. Further MD investigations starting with preexisting anti-Frenkel pairs revealed recombination of all pairs within t rec < 1 ps, even for the case of neutral vacancies and charged interstitials, for which formally there is no electrostatic attraction between the defects. In conclusion, we find no physically reasonable route to generating point-defects in HfO 2 by an applied field.

Over the past decades, studies on the biology of human adenoviruses (HAdVs) mainly focused on the HAdV prototype species C type 5 (HAdV-C5) and revealed fundamental molecular insights into mechanisms of viral replication and viral cell transformation. Recently, other HAdV species are gaining more and more attention in the field. Reports on large E1B proteins (E1B-55K) from different HAdV species showed that these multifactorial proteins possess strikingly different features along with highly conserved functions. In this work, we identified potential SUMO-conjugation motifs (SCMs) in E1B-55K proteins from HAdV species A to F. Mutational inactivation of these SCMs demonstrated that HAdV E1B-55K proteins are SUMOylated at a single lysine residue that is highly conserved among HAdV species B to E. Moreover, we provide evidence that E1B-55K SUMOylation is a potent regulator of intracellular localization and p53-mediated transcription in most HAdV species. We also identified a lysine residue at position 101 (K101), which is unique to HAdV-C5 E1B-55K and specifically regulates its SUMOylation and nucleo-cytoplasmic shuttling. Our findings reveal important new aspects on HAdV E1B-55K proteins and suggest that different E1B-55K species possess conserved SCMs while their SUMOylation has divergent cellular effects during infection. Importance E1B-55K is a multifunctional adenoviral protein and its functions are highly regulated by SUMOylation. Although functional consequences of SUMOylated HAdV-C5 E1B-55K are well studied, we lack information on the effects of SUMOylation on homologous E1B-55K proteins from other HAdV species. Here, we show that SUMOylation is a conserved post-translational modification in most of the E1B-55K proteins, similar to what we know about HAdV-C5 E1B-55K. Moreover, we identify subcellular localization and regulation of p53-dependent transcription as highly conserved SUMOylation-regulated E1B-55K functions. Thus, our results highlight how HAdV proteins might have evolved in different HAdV species with conserved domains involved in virus replication and differing alternative functions and interactions with the host cell machinery. Future research will link these differences and similarities to the diverse pathogenicity and organ tropism of the different HAdV species.

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