Restricted open-shell Kohn-Sham (ROKS) theory provides a powerful computational tool for calculating singlet excited state energies and dynamics. However, the possibility of multiple solutions to the ROKS equations - with the associated difficulty of automatically selecting the physically meaningful solution - limits its usefulness for intensive applications such as long-time Born-Oppenheimer molecular dynamics. We present an implementation of ROKS for excited states which prescribes the physically correct solution from an overlap criterion and guarantees that this solution is stationary, allowing for straightforward evaluation of nuclear gradients. The method is used to benchmark ROKS for vertical excitation energies of small and large organic dyes and for the calculation of Stokes shifts. With common density functional approximations, ROKS vertical excitation energies, and Stokes shifts show similar accuracy to those from time-dependent density functional theory and Δ-self-consistent-field approaches. Advantages of the ROKS approach for excited state structure and molecular dynamics are discussed.
Background: Successful outcomes of the Learning Assistant (LA) model include increased learning outcomes in STEM gateway courses and increased persistence to graduation among LAs and the students they serve. While there are many possible reasons that the LA program is effective, the pedagogical development of the LAs themselves has not yet been systematically studied. The research reported here investigated how deeply first-time LAs enrolled in a one-semester pedagogy course took up the language associated with the course's essential pedagogical principles. By reviewing prior research as well as assessing our target population and our pedagogy course learning goals, we developed a set of three essential pedagogical principles that are critical for effective classroom instruction and developed a coding scheme for identifying these principles in LAs' written work. We then looked at LA's development of language with respect to these principles by analyzing weekly teaching reflections submitted by LAs during five iterations of our pedagogy course. Results: Our research indicated that the language used to introduce particular pedagogical principles might play an important role in initiating LAs' uptake of these concepts. We found that LAs began to develop an understanding of the language that values students' prior ideas in learning, but the depth of this understanding varied. In addition, LAs did not demonstrate as much growth in their language with respect to the formative assessment or to the idea that students play a role in constructing knowledge. Conclusions: In developing a pedagogy course for LAs, relating to their prior backgrounds in STEM appears to be critical. Using language that is accessible seems to increase LAs' ability to develop pedagogical principles. Although LAs' development of language related to the essential pedagogical principles is small, it may be enough to allow them to create contexts that facilitate learning.
Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].
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