Statistical analysis of the performance of a variety of first-principles schemes for accurate prediction of binary semiconductor band gaps.

Standard density functional theory (DFT) approximations tend to strongly underestimate band gaps, while the more accurate GW and hybrid functionals are much more computationally demanding and unsuitable for high-throughput screening. In this work, we have performed an extensive benchmark of several approximations with different computational complexity [G0W0@PBEsol, HSE06, PBEsol, modified Becke-Johnson potential (mBJ), DFT-1/2, and ACBN0] to evaluate and compare their performance in predicting the bandgap of semiconductors. The benchmark is based on 114 binary semiconductors of different compositions and crystal structures, for about half of which experimental band gaps are known. Surprisingly, we find that, compared with G0W0@PBEsol, which exhibits a noticeable underestimation of the band gaps by about 14%, the much computationally cheaper pseudohybrid ACBN0 functional shows a competitive performance in reproducing the experimental data. The mBJ functional also performs well relative to the experiment, even slightly better than G0W0@PBEsol in terms of mean absolute (percentage) error. The HSE06 and DFT-1/2 schemes perform overall worse than ACBN0 and mBJ schemes but much better than PBEsol. Comparing the calculated band gaps on the whole dataset (including the samples with no experimental bandgap), we find that HSE06 and mBJ have excellent agreement with respect to the reference G0W0@PBEsol band gaps. The linear and monotonic correlations between the selected theoretical schemes and experiment are analyzed in terms of the Pearson and Kendall rank coefficients. Our findings strongly suggest the ACBN0 and mBJ methods as very efficient replacements for the costly G0W0 scheme in high-throughput screening of the semiconductor band gaps.

Prediction of novel two-dimensional Dirac nodal line semimetals in Al2B2 and AlB4 monolayers.

Topological semimetal phases in two-dimensional (2D) materials have gained widespread interest due to their potential applications in novel nanoscale devices. Despite the growing number of studies on 2D topological nodal lines (NLs), candidates with significant topological features that combine nontrivial topological semimetal phase with superconductivity are still rare. Herein, we predict Al2B2 and AlB4 monolayers as new 2D nonmagnetic Dirac nodal line semimetals with several novel features. Our extensive electronic structure calculations combined with analytical studies reveal that, in addition to multiple Dirac points, these 2D configurations host various highly dispersed NLs around the Fermi level, all of which are semimetal states protected by time-reversal and in-plane mirror symmetries. The most intriguing NL in Al2B2 encloses the K point and crosses the Fermi level, showing a considerable dispersion and thus providing a fresh playground to explore exotic properties in dispersive Dirac nodal lines. More strikingly, for the AlB4 monolayer, we provide the first evidence for a set of 2D nonmagnetic open type-II NLs coexisting with superconductivity at a rather high transition temperature. The coexistence of superconductivity and nontrivial band topology in AlB4 not only makes it a promising material to exhibit novel topological superconducting phases, but also a rather large energy dispersion of type-II nodal lines in this configuration may offer a platform for the realization of novel topological features in the 2D limit.

An in vitro study of antileishmanial effect of Portulaca oleracea extract.

BACKGROUND & OBJECTIVES: Leishmaniasis is caused by protozoa of Leishmania genus and is considered as a zoonotic disease. It is a major public health problem worldwide, with high endemicity in developing countries like Iran. Various chemical drugs are used for leishmaniasis treatment, but their side-effects and the emergence of drug resistance have led to look for new effective compounds. The aim of this study was to introduce purslane (Portulaca oleracea) as a traditional and medicinal herb which might act as a valuable source for designing new pharmaceutical drug/lead against Leishmania sp. METHODS: This study was conducted in the laboratory of Seddigheh Tahereh Infectious Disease Research Center, Isfahan, Iran during the spring of 2015. The essence from the purslane plant was prepared through water distillation and the alcoholic extract was prepared through maceration method. The essence was dried, and diluted with DMSO (5%). Leishmania major promastigotes were cultured in 25 ΁ 2΀C temperature in the stationary phase of RPMI-1640 medium, enriched with 10% fetal calf serum and penicillin-streptomycin to yield higher quantity. The biological activity of herb essence was evaluated on L. major promastigotes and compared to glucantime reference drug using methylthiazole tetrazolium (MTT) colorometric assay. The optical density absorbance was measured with Eliza reader set, and the IC50 value was calculated at different time intervals. All tests were repeated thrice. Results were analyzed by using Tukey test and t-test. RESULTS: The IC50 values after 48 h, for glucantime against standard parasite promastigotes and clinical strains were equal to 12 and 19 mg/ml, respectively, whereas for purslane herb leaves and stems essence; it was equal to 360 and 680 mg/ml, respectively. Although, the glucantime pharmaceutical drug was more efficient compared to the investigated herb essence, the essense had significant effect on L. major promastigotes with increasing density (p <0.05). The ingredients of the herb leaves and stem essence were-Phytol, squalene, palmitic acid, ethyl- linoleate, ferulic acid, linolenic acid, scopoletin, linoleic acid, rhein, apigenin, and bergapten. INTERPRETATION & CONCLUSION: The study showed that essence of purslane has considerable antileishmanial effects and can stop the growth of parasites in the laboratory compared to glucantime. More experiments are necessary to investigate its effect on Leishmania parasite in animal model.