83 research outputs found
Integral-direct Hartree-Fock and M{\o}ller-Plesset Perturbation Theory for Periodic Systems with Density Fitting: Application to the Benzene Crystal
We present an algorithm and implementation of integral-direct, density-fitted
Hartree-Fock (HF) and second-order M{\o}ller-Plesset perturbation theory (MP2)
for periodic systems. The new code eliminates the formerly prohibitive storage
requirements and allows us to study systems one order of magnitude larger than
before at the periodic MP2 level. We demonstrate the significance of the
development by studying the benzene crystal in both the thermodynamic limit and
the complete basis set limit, for which we predict an MP2 cohesive energy of
kJ/mol, which is about -- kJ/mol larger in magnitude than all
previously reported MP2 calculations. Compared to the best theoretical estimate
from literature, several modified MP2 models approach chemical accuracy in the
predicted cohesive energy of the benzene crystal and hence may be promising
cost-effective choices for future applications on molecular crystals.Comment: 5 pages (w/o refs or SI), 3 figures, 1 tabl
Interplay between local moment and itinerant magnetism in the layered metallic antiferromagnet TaFeTe
Two-dimensional (2D) antiferromagnets have garnered considerable interest for
the next generation of functional spintronics. However, many available bulk
materials from which 2D antiferromagnets are isolated are limited by their
sensitivity to air, low ordering temperatures, and insulating transport
properties. TaFeTe offers unique opportunities to address these
challenges with increased air stability, metallic transport properties, and
robust antiferromagnetic order. Here, we synthesize TaFeTe ( =
0.14), identify its structural, magnetic, and electronic properties, and
elucidate the relationships between them. Axial-dependent high-field
magnetization measurements on TaFeTe reveal saturation magnetic
fields ranging between 27-30 T with a saturation magnetic moment of 2.05-2.12
. Magnetotransport measurements confirm TaFeTe is metallic
with strong coupling between magnetic order and electronic transport.
Angle-resolved photoemission spectroscopy measurements across the magnetic
transition uncover a complex interplay between itinerant electrons and local
magnetic moments that drives the magnetic transition. We further demonstrate
the ability to isolate few-layer sheets of TaFeTe through
mechanical exfoliation, establishing TaFeTe as a potential
platform for 2D spintronics based on metallic layered antiferromagnets.Comment: 30 pages, 5 main figures, 23 supporting figures, and 3 supporting
table
A Census of rRNA Genes and Linked Genomic Sequences within a Soil Metagenomic Library
We have analyzed the diversity of microbial genomes represented in a library of metagenomic DNA from soil. A total of 24,400 bacterial artificial chromosome (BAC) clones were screened for 16S rRNA genes. The sequences obtained from BAC clones were compared with a collection generated by direct PCR amplification and cloning of 16S rRNA genes from the same soil. The results indicated that the BAC library had substantially lower representation of bacteria among the Bacillus, α-Proteobacteria, and CFB groups; greater representation among the β- and γ-Proteobacteria, and OP10 divisions; and no rRNA genes from the domains Eukaryota and Archaea. In addition to rRNA genes recovered from the bacterial divisions Proteobacteria, Verrucomicrobia, Firmicutes, Cytophagales, and OP11, we identified many rRNA genes from the BAC library affiliated with the bacterial division Acidobacterium; all of these sequences were affiliated with subdivisions that lack cultured representatives. The complete sequence of one BAC clone derived from a member of the Acidobacterium division revealed a complete rRNA operon and 20 other open reading frames, including predicted gene products involved in cell division, cell cycling, folic acid biosynthesis, substrate metabolism, amino acid uptake, DNA repair, and transcriptional regulation. This study is the first step in using genomics to reveal the physiology of as-yet-uncultured members of the Acidobacterium division
Bacterial ecology of ancient Saharan salt-enrichment ponds at Teguidda-n-Tessoumt
The original publication is available at www.interscience.wiley.co
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