We have developed a cluster model of a TiO(2) nanoparticle in the dye-sensitized solar cell and used first-principles quantum chemistry, coupled with a continuum solvation model, to compute structures and energetics of key electronic and structural intermediates and transition states. Our results suggest the existence of shallow surface trapping states induced by small cations and continuum solvent effect as well as the possibility of the existence of a surface band which is 0.3-0.5 eV below the conduction band edge. The results are in uniformly good agreement with experiment and establish the plausibility of an ambipolar model of electron diffusion in which small cations, such as Li(+), diffuse alongside the current carrying electrons in the device, stabilizing shallowing trapping states, facilitating diffusion from one of these states to another, in a fashion that is essential to the functioning of the cell.
Recent advances in graphics-processing-unit (GPU) hardware and improved efficiencies of atomistic simulation programs allow the screening of a large number of polymers to predict properties that require running and analyzing long Molecular Dynamics (MD) trajectories of large molecular systems. This paper outlines an efficient MD cooling simulation workflow based on GPU MD simulation and the refined Optimized Potentials for Liquids Simulation (OPLS) OPLS3e force field to calculate glass transition temperatures (T<sub>g</sub>) of 315 polymers for which experimental values were reported by Bicerano.<sup>1</sup> We observed good agreement of predicted T<sub>g</sub> values with experimental observation across a wide range of polymers, which confirms the clear utility of the described workflow. During the stepwise cooling simulation for the calculation of T<sub>g</sub>, a subset of polymers clearly showed an ordered structure developing as the temperature decreased. Such polymers have a point of discontinuity on the specific volume vs. temperature plot, which we associated with the melting temperature (T<sub>m</sub>). We demonstrate the distinction between crystallized and amorphous polymers by examining polyethylene. Linear polyethylene shows a discontinuity in the specific volume vs. temperature plot, but we do not observe the discontinuity for branched polyethylene simulations.
Design and development of highly efficient organic and organometallic dopants is one of the central challenges in the organic light-emitting diodes (OLEDs) technology. Recent advances in the computational materials science have made it possible to apply computer-aided evaluation and screening framework directly to the design space of organic lightemitting diodes (OLEDs). In this work, we will showcase two major components of the latest in silico framework for development of organometallic phosphorescent dopants – (1) rapid screening of dopants by machine-learned quantum mechanical models and (2) phosphorescence lifetime predictions with spin-orbit coupled calculations (SOC-TDDFT). The combined work of virtual screening and evaluation would significantly widen the design space for highly efficient phosphorescent dopants with unbiased measures to evaluate performance of the materials from first principles.
To the Editor. —I wish to commend Drs Bellet and Maloney on their excellent article reviewing the importance of empathy as a tool in medical practice.1In total, it was a timely review of a critical issue in medicine. Unfortunately, I fear that the authors may have inadvertently prejudiced the character of empathy when they limited their comments to the nature of compassion as a clinical device. The social revolution that is rapidly enveloping the field of medicine is not designed to produce physicians who are merely aware of the mechanism for acting in an empathetic manner, but, rather, it hopes to develop physicians who can remain both profoundly human and professionally competent in the clinical setting. Patients cannot be satisfied by a physician who is merely capable of offering some sort of placebo perfunctory conciliation in times of crises for, as with any placebo, when patients realize
Average ligand removal enthalpies of 30 differently coordinated mono-nuclear fourth-row transition metal complexes taken from a database recently considered by Johnson and Becke [Can. J. Chem., 2009, 8, 1369] have been computed in the gas phase using unrestricted pseudo-spectral (LACV3P) and fully analytic (qzvp(-g)) B3LYP including a recently developed empirical dispersion correction. Heats of formation of neutral singlet reactants and neutral, potentially high spin, products have been taken from NIST's Organometallic Thermochemistry Database. Comparison of B3LYP-MM//qzvp(-g) and experimental average ligand removal enthalpies reveals a systematic error in the reported experimental enthalpies for manganese-containing complexes which is verified with high-level, CCSD(T)-F12//family of cc-pVTZ, explicitly correlated coupled-cluster methods. Other B3LYP-MM//qzvp(-g) error patterns give rise to a d-block localized orbital correction (DBLOC) scheme containing six transferable parameters that correct the functional's description of metal–ligand bonding, cation-π, and dispersion interactions as well as metal and/or ligand multi-reference effects. Metal–ligand cation-π and dispersion interactions have been fit to the monopole/induced-dipole, , and induced-dipole/induced-dipole, , interaction functions, respectively. This DBLOC model has been built upon a previously determined set of metal atom parameters which are necessary to properly describe the free metal atom reaction products. The final DBLOC model brings the mean unsigned error of B3LYP-MM//qzvp(-g) from 3.74 ± 3.51 kcal/mol to 0.94 ± 0.68 kcal/mol and corrects the functional's under binding in nearly every case. Several important connections among DBLOC parameters have been made.
Abstract We studied the development of Pacific madrone (Arbutus menziesii) sprout clumps of various initial densities and their effect on Douglas-fir (Pseudotsuga menziesii) seedling growth and understory vegetation. Five years after density treatments, average leaf area index (LAI) of 9-year-oldmadrone sprouts ranged from 3.6-1.0 m²/m² and total aboveground biomass from 25,630-8,390 kg/ha on the high- and low-density plots, respectively. Diameter of 9-year-old Douglas-fir was inversely related to madrone LAI and ranged from about 27 mm on the high-density plots to 54 mmin the absence of madrone. Analyses of diameter growth trends also indicated that, in the absence of madrone, Douglas-fir grew significantly (P = 0.001 to 0.023) faster than in other treatments. An index of shrub, forb, and grass density was inversely related to madrone LAI, suggesting thatunderstory species are quickly excluded from young madrone stands during secondary succession. We provide equations relating the 5-year growth of 9-year-old Douglas-fir to measures of madrone density and seedling size made when the plantation was 5 years old. West. J. Appl. For. 5(1):20-24.
Amorphous solid dispersions (ASDs) are commonly used to orally deliver small-molecule drugs that are poorly water-soluble. ASDs consist of drug molecules in the amorphous form which are dispersed in a hydrophilic polymer matrix. Producing a high-performance ASD is critical for effective drug delivery and depends on many factors such as solubility of the drug in the matrix and the rate of drug release in aqueous medium (dissolution), which is linked to bioperformance. Often, researchers perform a large number of design iterations to achieve this objective. A detailed molecular-level understanding of the mechanisms behind ASD dissolution behavior would aid in the screening, designing, and optimization of ASD formulations and would minimize the need for testing a wide variety of prototype formulations. Molecular dynamics and related types of simulations, which model the collective behavior of molecules in condensed phase systems, can provide unique insights into these mechanisms. To study the effectiveness of these simulation techniques in ASD formulation dissolution, we carried out dissipative particle dynamics simulations, which are particularly an efficient form of molecular dynamics calculations. We studied two stages of the dissolution process: the early-stage of the dissolution process, which focuses on the dissolution at the ASD/water interface, and the late-stage of the dissolution process, where significant drug release would have occurred and there would be a mixture of drug and polymer molecules in a predominantly aqueous environment. Experimentally, we used Fourier transform infrared spectroscopy to study the interactions between drugs, polymers, and water in the dry and wet states and the chromatographic technique to study the rate of drug and polymer release. Both experiments and simulations provided evidence of polymer microstructures and drug–polymer interactions as important factors for the dissolution behavior of the investigated ASDs, consistent with previous work by Pudlas et al. (Eur. J. Pharm. Sci. 2015, 67, 21–31). As experimental and simulation results are consistent and complementary, it is clear that there is significant potential for combined experimental and computational research for a detailed understanding of ASD formulations and, hence, formulation optimization.
The mechanism of water oxidation by a single site ruthenium oxygen evolving complex is investigated using fully unrestricted pseudospectral B3LYP with the effective core potential LACV3P in continuum solvent with some quantum mechanical waters. Guess wave functions have been used that allow greater flexibility in sampling different electronic configurations of the complex. Systematic comparison with experiment is improved using these guesses because they provide a complete analysis of the low energy manifold and help to alleviate the formal disconnect between theory and experiment in assigning Lewis structures for transition metal complexes. In agreement with results from the literature, the challenging 4e(-)and 4H(+) oxidation of water is accomplished using a mechanism that features three proton coupled electron transfers, one electron transfer, one atom proton transfer (APT), and one ligand exchange (LE). Calculations on a large database of ruthenium complexes allows us to benchmark the computation of reduction half potentials and free energies of activation and to investigate systematic ligand variations and their effect on the reaction mechanism. Mean unsigned errors of reduction half potentials in comparison to experiment are generally small (100-200 mV). The APT and LE steps are found to be rate limiting with free energy barriers of 19.27 and 19.53 kcal/mol respectively, which is in excellent agreement with the ∼20 kcal/mol barrier obtained from experimental rate constants using classical transition state theory.
Journal Article Couldn't be different Get access THOMAS F. HUGHES, M.B.A. THOMAS F. HUGHES, M.B.A. Visiting Associate Professor of Pharmacy Administration School of Pharmacy, University of North Carolina at Chapel Hill; at the time of this presentation, he was Director of Pharmacy, North Carolina Memorial Hospital, Chapel Hill, NC. Search for other works by this author on: Oxford Academic Google Scholar American Journal of Hospital Pharmacy, Volume 46, Issue 12, 1 December 1989, Pages 2520–2521, https://doi.org/10.1093/ajhp/46.12.2520 Published: 01 December 1989
