We investigate the electronic properties of bilayer MoS2 exposed to an external electric field by using first-principles calculations. It is found that a larger interlayer distance, referring to that by standard density functional theory (DFT) with respect to that by DFT with empirical dispersion corrections, makes indirect-direct band gap transition possible by electric control. We show that external electric field effectively manipulates the valence band contrast between the K- and Γ-valleys by forming built-in electric dipole fields, which realizes an indirect-direct transition before a semiconductor-metal transition happens. Our results provide a novel efficient access to tune the electronic properties of two-dimensional layered materials.
Linkage disequilibrium (LD) plays an important role in genomic selection and mapping quantitative trait loci (QTL). In this study, the pattern of LD and effective population size (Ne) were investigated in Chinese beef Simmental cattle. A total of 640 bulls were genotyped with IlluminaBovinSNP50BeadChip and IlluminaBovinHDBeadChip. We estimated LD for each autosomal chromosome at the distance between two random SNPs of <0 to 25 kb, 25 to 50 kb, 50 to 100 kb, 100 to 500 kb, 0.5 to 1 Mb, 1 to 5 Mb and 5 to 10 Mb. The mean values of r2 were 0.30, 0.16 and 0.08, when the separation between SNPs ranged from 0 to 25 kb to 50 to 100 kb and then to 0.5 to 1 Mb, respectively. The LD estimates decreased as the distance increased in SNP pairs, and increased with the increase of minor allelic frequency (MAF) and with the decrease of sample sizes. Estimates of effective population size for Chinese beef Simmental cattle decreased in the past generations and Ne was 73 at five generations ago.
Deep
ultraviolet (UV) nonlinear optical (NLO) materials
are of
intense interest owing to their broad technological applications from
laser photolithography to semiconductor manufacturing, biomedicine,
and attosecond pulse generation. To date, deep UV NLO materials are
still scarce due to the multiple rigorous criteria that should be
fulfilled. Using evolutionary crystal structure prediction combined
with first-principles calculations, we systematically explored the
pseudobinary Li2O–B2O3 system
and predicted twenty-four metastable structures in the Li2O–B2O3 system. We found that four structures
of LiBO2, e.g., oC16, oP16-1, oP16-2, and mP16, are promising
deep UV NLO crystals. Among them, oC16-LiBO2, oP16-2-LiBO2, and mP16-LiBO2 exhibit significantly large SHG coefficients
(>6 KDP), moderate birefringence (∼0.12@1064 nm), and suitable
band gaps (∼7 eV). Importantly, the oC16-LiBO2 structure is expected to be synthesized experimentally as
its formation energy is lower than that of γ-LiBO2.
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