A modification of the nudged elastic band method for finding minimum energy paths is presented. One of the images is made to climb up along the elastic band to converge rigorously on the highest saddle point. Also, variable spring constants are used to increase the density of images near the top of the energy barrier to get an improved estimate of the reaction coordinate near the saddle point. Applications to ${\mathrm{CH}}_{\mathrm{4}}$ dissociative adsorption on Ir(111) and ${\mathrm{H}}_{\mathrm{2}}$ on Si(100) using plane wave based density functional theory are presented.

Preventing Radiation Damage: Inside a nuclear reactor, long-term exposure to radiation causes structural damage and limits the lifetimes of the reactor components. Bai et al. (p. 1631 ; see the Perspective by Ackland ) now show, using three simulation methods able to cover a wide range of time and length scales, that grain boundaries in copper can act as sinks for radiation-induced defects. The boundaries are able to store up defects, in the form of interstitials, which subsequently annihilate with vacancies in the bulk. This recombination mechanism has a lower energy barrier than the bulk equivalent, and so provides a lower-cost route for the copper to self-heal.

Designing a material from the atomic level to achieve a tailored response in extreme conditions is a grand challenge in materials research. Nanostructured metals and composites provide a path to this goal because they contain interfaces that attract, absorb and annihilate point and line defects. These interfaces recover and control defects produced in materials subjected to extremes of displacement damage, impurity implantation, stress and temperature. Controlling radiation-induced-defects via interfaces is shown to be the key factor in reducing the damage and imparting stability in certain nanomaterials under conditions where bulk materials exhibit void swelling and/or embrittlement. We review the recovery of radiation-induced point defects at free surfaces and grain boundaries and stabilization of helium bubbles at interphase boundaries and present an approach for processing bulk nanocomposites containing interfaces that are stable under irradiation.United States. Dept. of Energy. Office of Basic Energy Sciences (Award 2008LANL1026

We employ a combination of first-principles calculations and optical characterization experiments to explain the mechanism by which Ga${}^{3+}$ doping prevents the trapping of free carriers due to shallow traps in RE${}_3$Al${}_5$O${}_{12}$ garnet scintillators (where RE represents a $3+$ rare-earth cation). Specifically, we confirm that Ga${}^{3+}$ doping does not reduce the defect concentration (defect engineering), but rather leads to shifts in the valence and conduction bands such that the energy level of shallow defects is no longer in the forbidden gap where electrons can be trapped (band-gap engineering).