We report data for I-band surface brightness Ñuctuation (SBF) magnitudes, (V [I) colors, and distance moduli for 300 galaxies. The survey contains E, S0, and early-type spiral galaxies in the proportions of 49 : 42 : 9 and is essentially complete for E galaxies to Hubble velocities of 2000 km s~1, with a substantial sampling of E galaxies out to 4000 km s~1. The median error in distance modulus is 0.22 mag. We also present two new results from the survey. (1) We compare the mean peculiar Ñow velocity (bulk Ñow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and we Ðnd very good agreement with cold, dark matter cosmologies if the transfer function scale parameter ! and the power spectrum normalization are related by Derived p 8 p 8 !~0.5 B 2^0.5. directly from velocities, this result is independent of the distribution of galaxies or models for biasing. This modest bulk Ñow contradicts reports of large-scale, large-amplitude Ñows in the D200 Mpc diameter volume surrounding our survey volume. (2) We present a distance-independent measure of absolute galaxy luminosity, and show how it correlates with galaxy properties such as color and velocity dis-N persion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.
To evaluate the potential of Na-ion batteries, we contrast in this work the difference between Na-ion and Li-ion based intercalation chemistries in terms of three key battery properties -voltage, phase stability and diffusion barriers. The compounds investigated comprise the layered AMO 2 and AMS 2 structures, the olivine and maricite AMPO 4 structures, and the NA-SICON A 3 V 2 (PO 4 ) 3 structures. The calculated Na voltages for the compounds investigated are 0.18-0.57 V lower than that of the corresponding Li voltages, in agreement with previous experimental data. We believe the observed lower voltages for Na compounds are predominantly a cathodic effect related to the much smaller energy gain from inserting Na into the host structure compared to inserting Li. We also found a relatively strong dependence of battery properties with structural features. In general, the difference between the Na and Li voltage of the same compound, ∆V Na-Li , is less negative for the maricite structures preferred by Na, and * To whom correspondence should be addressed 1 more negative for the olivine structures preferred by Li. The layered compounds have the most negative ∆V Na-Li . In terms of phase stability, we found that open structures, such as the layered and NASICON structures that are better able to accommodate the larger Na + ion generally have both Na and Li versions of the same compound. For the close-packed AMPO 4 structures, our results show that Na generally prefers the maricite structure, while Li prefers the olivine structure, in agreement with previous experimental work. We also found surprising evidence that the barriers for Na + migration can potentially be lower than that for Li + migration in the layered structures. Overall, our findings indicate that Na-ion systems can be competitive with Li-ion systems.
Standard approximations to the density functional theory exchange-correlation functional have been extraordinary successful, but calculating formation enthalpies of reactions involving compounds with both localized and delocalized electronic states remains challenging. In this work we examine the shortcomings of the generalized gradient approximation (GGA) and GGA + U in accurately characterizing such difficult reactions. We then outline a methodology that mixes GGA and GGA + U total energies (using known binary formation data for calibration) to more accurately predict formation enthalpies. We demonstrate that for a test set of 49 ternary oxides, our methodology can reduce the mean absolute relative error in calculated formation enthalpies from approximately 7.7-21% in GGA + U to under 2%. As another example we show that neither GGA nor GGA + U alone accurately reproduces the Fe-P-O phase diagram; however, our mixed methodology successfully predicts all known phases as stable by naturally stitching together GGA and GGA + U results. As a final example we demonstrate how our technique can be applied to the calculation of the Li-conversion voltage of LiFeF 3 . Our results indicate that mixing energies of several functionals represents one avenue to improve the accuracy of total energy computations without affecting the cost of calculation.
Phosphate materials are being extensively studied as lithium-ion battery electrodes. In this work, we present a highthroughput ab initio analysis of phosphates as cathode materials. Capacity, voltage, specific energy, energy density, and thermal stability are evaluated computationally on thousands of compounds. The limits in terms of gravimetric and volumetric capacity inherent to the phosphate chemistry are determined. Voltage ranges for all redox couples in phosphates are provided, and the structural factors influencing the voltages are analyzed. We reinvestigate whether phosphate materials are inherently safe and find that, for the same oxidation state, oxygen release happens thermodynamically at lower temperature for phosphates than for oxides. These findings are used to recommend specific chemistries within the phosphate class and to show the intrinsic limits of certain materials of current interest (e.g., LiCoPO 4 and LiNiPO 4 ).
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