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We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact.
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Quantum transport in conductive bacterial nanowires
The electrical properties of conductive heme-based nanowires found in the pili in Geobacter sulfurreducens bacteria were investigated using a density functional theory (DFT) model. Green’s function methods were used to calculate quantum transmission and single molecule conductance in both the low temperature (coherent) and room temperature (decoherent) regimes. Several approaches were attempted for modeling the energy levels of the heme-sites, including semi-empirical methods, and quantum transmission was calculated at several different length scales. This result was compared to experimental findings as well as other modeling results for similar cytochrome structures, such as electron hopping models applied to neighboring heme sites. The results show that coordinated hemes prefer a low spin state with electron delocalization over the porphyrin rings and coordinating histidine groups from the protein scaffold. Orbital overlap between heme centers was shown to have a significant impact on quantum transport, with perpendicular heme centers having a rate limiting effect on transport. Semi-empirical models such as the extended Hückel method were found to be inaccurate for modeling transport, showing the importance of electron-electron repulsion and a more detailed model for the organometallic bonding.
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- Award ID(s):
- 2036865
- PAR ID:
- 10486901
- Publisher / Repository:
- IEEE
- Date Published:
- Journal Name:
- 2021 IEEE 16th Nanotechnology Materials and Devices Conference (NMDC)
- ISBN:
- 9781665418928
- Format(s):
- Medium: X
- Location:
- Vancouver, BC
- Sponsoring Org:
- National Science Foundation
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