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Using first-principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA), the electronic and thermoelectric properties of KCaF3 are calculated. The electronic structure calculated with GGA shows that KCaF3 is an insulator. The thermoelectric properties of KCaF3 are computed as a function of chemical potential μ and charge carrier concentrations (1018–1022 cm−3). Both hole and electron doping decrease the absolute value of Seebeck coefficient. The calculated power factor shows that p-type KCaF3 has a larger power factor at the optimized charge carriers. The maximum figure of merit (ZT) occurs around 1021 cm−3 hole carrier concentrations and the largest value of ZT ∼0.7 is achieved at 800 K. When KCaF3 is doped with electron, the maximum ZT occurs around 1020 cm−3 and the largest value of ZT at 800 K is about 0.4. Hence, high ZT in KCaF3 is possible at high hole carrier concentrations as compared with electron carrier concentrations. Compared with n-type KCaF3, p-type KCaF3 has good thermoelectric properties, which are attributed to larger effective mass and low thermal conductivity of holes.

Elemental doping is considered to be an effective strategy to improve the photoelectrochemical (PEC) activity of hematite (α-Fe2O3) as a photoanode for water splitting, but the precise function (s) of the dopant remains unclear. In this study, we report on the structural and charge separation properties of titanium-doped hematite (Ti doped Fe2O3) films prepared by a simple electrospray technique for PEC water oxidation. The effect of Ti doping on the structure, morphology, light absorption, and electrical and photoelectrochemical properties was investigated on α-Fe2O3 films. SEM images revealed a reduction in particle sizes for 2% Ti doped α-Fe2O3, while an increase in particle size was observed for higher Ti content. XRD confirmed the presence of α-Fe2O3 without any impurity or other phases. From XPS spectra, the incorporation of Ti was confirmed in the form of Ti4+ as predominant species while no impurities from the substrate were detected. When the Ti doped Fe2O3 (2% Ti) film was used as a photoanode in a PEC cell, it delivered the best performance with a maximum photocurrent density of 1.09 mA cm−2 (at 1.8 V vs. RHE and under standard 1 sun illumination conditions (AM 1.5 G, 100 mW cm−2)), which is 2 times higher than that of the un-doped α-Fe2O3 (0.51 mA cm−2). The photoelectrode also showed a superior incident photon to current efficiency (IPCE) as compared to an un-doped α-Fe2O3. This enhancement in performance was attributed to the better charge separation and transport properties of α-Fe2O3 due to Ti doping, as revealed by an electrochemical impedance spectroscopy (EIS) analysis.

Controlling oxygen vacancy in undoped SrTiO3 was used to realize the phonon-glass electron-crystal (PGEC) concept. The undoped SrTiO3 samples were synthesized through solid-state-reaction method in air and then reduced through annealing under low oxygen partial pressure conditions. We show that decreasing the oxygen partial pressure (Po2) results in increase of the electrical conductivity, and the oxygen vacancies act as phonon scattering centers, which lead to decrease in the lattice thermal conductivity. Both the enhanced electrical conductivity (σ) and reduced thermal conductivity (κ) were achieved simultaneously through oxygen vacancy in undoped SrTiO3. This significantly increases the ratio of σ/κ that results in an enormously enhanced ZT value of about 13 times larger as compared with the samples reduced under relatively high Po2. Density-functional theory calculations also reveal that oxygen vacancies in SrTiO3 reduce the band-gap, and consequently increase the electrical conductivity.

Made available in DSpace on 2021-06-25T11:08:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 This research study reports the formation of flexible and multifunctional organic-inorganic hybrid membranes (BC-SiO2-TiO2/Ag) based on bacterial cellulose (BC) that contain photoactive (TiO2) and antibacterial (Ag) components, rendering them photocatalytic, self-cleaning and UV-shielding properties (due to TiO2) as well as antibacterial activity. Coating of BC with sol-gel derived silica and titania particles was achieved through hydrolysis-polycondensation of tetraethyl orthosilicate and titanium (IV) isopropoxide, respectively, and a soft hydrothermal treatment (140 °C, 20 h) was used to obtain well-crystalline TiO2. The prepared BC-SiO2-TiO2/Ag photoactive membranes were characterized by an array of analytical techniques including XRD, XRF, SEM-EDS, electronic absorption spectroscopy and vibrational spectroscopy. The morphology of TiO2 coatings changes from a homogenous film-like smooth one to a rougher one consisting of randomly oriented titania particles (170 ± 35 nm) upon increasing the TiO2 loading of the membranes. These prepared photoactive BC-SiO2-TiO2 membranes exhibited excellent TiO2-loading dependent photocatalytic/self-cleaning activity towards crystal violet dye deposited as an over-layer on the surface of the membranes, degrading 97 % of the dye within 50 min of UV illumination. In addition to good photoactivity, the BC-SiO2-TiO2/Ag membranes demonstrated reasonable antibacterial activity against five different bacterial strains under dark conditions. These flexible BC-based hybrid membranes with photocatalytic, self-cleaning, antibacterial properties have the potential to be used in the design of self-cleaning and antibacterial surfaces, filters and facemasks that could be easily disinfected under UV irradiation from a lamp or natural sunlight and safely discarded and even recycled. Institute of Chemical Sciences University of Peshawar Institute of Chemistry São Paulo State University - UNESP, CP 355 Government Girls Degree College Institute of Research and Development Duy Tan University Institute of Physics Federal University of Mato Grosso do Sul Institute of Chemistry São Paulo State University - UNESP, CP 355

\textit{Ab-initio} calculations based on density functional theory with local spin density approximation are used to study defects-driven magnetism in bulk $\alpha$-Li$ _{3}$N. Our calculations show that bulk Li$ _{3} $N is a non-magnetic semiconductor. Two types of Li vacancies (Li-I and Li-II) are considered, and Li-vacancies (either Li-I or Li-II type) can induce magnetism in Li$ _{3}$N with a total magnetic moment of 1.0 $\mu_{\rm B}$ which arises mainly due to partially occupied N-$p$-orbitals around the Li vacancies. The defect formation energies dictate that Li-II vacancy, which is in the Li$ _{2}$N plane, is thermodynamically more stable as compared with Li-I vacancy. The electronic structures of Li-vacancies show half-metallic behavior. On the other hand N-vacancy does not induce magnetism and has a larger formation energy than Li-vacancies. N vacancy derived bands at the Fermi energy are mainly contributed by the Li atoms. Carbon is also doped at Li-I and Li-II sites, and it is expected that doping C at Li-I site is thermodynamically more stable as compared with Li-II site. Carbon can induce metallicity with zero magnetic moment when doped at Li-I site, whereas magnetism is observed when Li-II site is occupied by the C impurity atom and C-driven magnetism is spread over the N atoms as well. Carbon can also induce half-metallic magnetism when doped at N site in Li$ _{3}$N, and has a smaller defect formation energy as compared with Li-II site doping. The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the C atoms is also investigated, and we conclude that FM state is more stable than the AFM state., Comment: Accepted; J. Mag. Mag. Mat. (2018)

The production of hydrogen, the future fuel, on stable, efficient, and robust electrocatalysts represents an attractive approach for the conversion and storage of carbon-free energy resources. In this study, earth-abundant nickel sulfide (NiS) electrocatalyst were grown on fluorine-doped tin oxide (FTO) substrate by a simple and cost-effective chemical bath deposition for hydrogen evolution reaction (HER). Energy dispersive X-ray analysis and X-ray photoelectron spectra indicated the presence of highly pure NiS. The HER performance of the catalyst was examined in alkaline solution (1.0 M NaOH; pH = 13.5). Notably, NiS film prepared at 100 °C demonstrated superior HER activity with an overpotential of 290 mV to afford a current density of 10 mA/cm2 and a Tafel slope of 143.4 mV/dec which are among the promising results obtained for sulfide-based HER electrocatalysts. The catalyst exhibited 100% faradaic efficiency and electrochemical stability which indicate its potential as noble-metal-free HER electrocatalyst.

Solar-driven carbon dioxide (CO2) conversion has gained tremendous attention as a prominent strategy to simultaneously reduce the atmospheric CO2 concentration and convert solar energy into solar fuels in the form of chemical bonds. Numerous efforts have been devoted to diverse photo-driven processes for CO2 conversion, which utilized a multidisciplinary strategy. Among them, the architecture of nanostructured metal-based catalysts is emerging as an eminent solution for the design of catalysts of this field. In this work, we first provide fundamental mechanisms of photochemical, photoelectrochemical, photothermal, and photobio(electro)chemical CO2 reduction processes to achieve an in-deep understanding of vital aspects. Importantly, the recent progress in the catalyst design for each reaction system is discussed and highlighted. Based on these analyses, an overview of photo-driven CO2 reduction on metal-based catalysts for solar fuel production is also spotlighted. Finally, we analyze challenges and prospects for the strategic direction of developments in the field.

Polythiophene (PTh) and graphene nanoplatelets (GNPs) nanocomposites with different ratio of GNPs (10–50 wt.%) were prepared by oxidative chemical polymerization technique and applied for the photocatalytic degradation of bromo phenol blue (BPB) and pathogen control. The as-prepared nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), UV–Vis spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The PTh-GNPs(50) achieved the highest photocatalytic degradation efficiency for BPB (94.1%) which was more than three times higher than that of the pristine PTh (31.3%). The enhanced photocatalytic activity of PTh-GNPs was attributed to the improved charge-transport and longer recombination time of e−/h+ pairs from PTh NPs to GNPs. Interestingly, PTh-GNPs(50) proved as a potent inhibitor against E.coli and S.aureus reported 18 mm zone of inhibition as compared to that of the control PTh (showing 9 mm and 5 mm zones of inhibition for the two strains, respectively) at 2000 µg/mL. These results make PTh-GNPs(50) nanocomposites a potential candidate for BPB removal and bacterial growth inhibition.

Thermoelectric properties of cubic (C) and tetragonal (T) BaTiO 3 (BTO) and PbTiO 3 (PTO) are investigated using density functional theory together with semiclassical Boltzmann's transport theory. Both electron and hole doped BTO and PTO are considered in 300–500 K temperature range. We observed that C-BTO has larger power factor( PF ) when doped with holes, whereas n-type carrier concentration in C-PTO has larger PF . Comparing both BTO and PTO, C-PTO has larger figure of merit ZT . Tetragonal distortion reduces the Seebeck coefficient S in n-doped PTO, and the electronic structures revealed that such reduction in S is mainly caused by the increase in the optical band gaps ( Γ − Γ and Γ-X).

In the search of high-performance cathodes for next-generation Li-ion batteries (LIBs), iron fluorides are among the most promising materials because of their extremely high theoretical capacity. This study reports on the synthesis, structural and electrochemical characterizations of cobalt doped iron fluoride hydrate as a high-performance cathode material for LIBs. A simple non-aqueous precipitation method is used to synthesize cobalt doped iron fluoride (Fe 0.9 Co 0.1 F 3 ·0.5H 2 O) while its structural and electrochemical properties are also evaluated. The thermogravimetric analysis reveals that the structure of the as-prepared material remains stable up to 243 °C. The structure was then found to collapse beyond this temperature due to the removal of water contents from the crystal structure. The material delivers a high discharge capacity of 227 mAh g −1 at 0.1C in the potential range of 1.8-4.5 V versus Li/Li + . The electrode retains a high reversible capacity of 150 mAh g −1 at a rate of 0.1C after 200 cycles, indicating high reversibility and stability of the material. The electrode also shows a superior rate capability of up to 10C, showing its potential use as a cathode material for LIBs.

In this work nickel modified polymer composites have been synthesized electrochemically for methanol electrooxidation on platinum and graphite electrodes. Ni (II) ions were incorporated on polyaniline and poly (o-aminophenol)(PANI/POAP) bilayer structure from 0.1 M Nickel sulphate hexahydrate solution at open circuit potential (OCP).TheNi (II) deposited composites were characterized with Fourier Transform Infrared (FTIR) spectroscopy, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Cyclic voltammetry characterization exhibits stable redox pair of Ni+3/Ni+2 for both electrodes. Fourier transform infrared spectroscopy was used for functional group analysis. Ni (II) peaks were observed in the region of 400–700 cm−1 along with peaks at 1102 cm−1 and 1400–1600 cm−1 for polyaniline and phenoxazine units. The Ni-polymer composite on platinum and graphite electrode followed different phenomenon for methanol electroxidation in alkaline media. The cyclic voltammetry results showed significantly large methanol oxidation on platinum substrate with charge storage capacity of 196 μ F/cm2 for 1.5 M methanol in alkaline media as compared to 8.306 μF/cm2 of graphite. The diffusion controlled linear response for increase rate of methanol concentration has been obtained for Ni (II)/PANI/POAP-Pt. The electrochemical impedance spectroscopy (EIS)results indicated increase in charge storage capacity from 10−4F/cm2 to 10−3 F/cm2 with increasing potentials at lower frequency region.The phase shift was observed from 60–40 degrees for increased potentials at low frequency range in EIS analysis. The increased conductive behavior from 10−5 to 10−2 s/cm2 has been obtained fornickel modified polymer composite at higher frequency region in EIS analysis.

In this study, we report on the direct growth of duel-faceted BiVO4 microcrystals on fluorine-doped tin oxide (FTO) coated glass by simple chemical bath deposition as photoanode material for PEC water oxidation. Crystal growth and particle density were affected by bath temperature; films grown in higher bath temperature (95 °C) showed great surface coverage and larger particle sizes, as indicated by scanning electron microscopy (SEM) images. X-ray diffraction (XRD) studies revealed that BiVO4 predominantly occurs in the form of monoclinic scheelite crystal structure in all deposited films. UV–vis spectroscopy and X-ray photoelectron spectroscopy (XPS) investigations confirmed the existence of pure BiVO4. High-temperature treatment of the film was found to improve crystallinity and preferential growth of dual-faceted ((010), (110)) BiVO4 microcrystals. An optimized electrode exhibited excellent PEC water oxidation performance, with 0.78 mA.cm−2 of photocurrent density at 1.23 V versus a reversible hydrogen electrode (RHE) under standard illumination (100 mW.cm−2 and AM 1.5), which was increased up to 1.23 mA.cm−2 before dark current started to flow. The electrode also showed good stability when exposed to longer illumination in a 0.5 M Na2SO4 solution, and n-type character. These findings are thus important for the development of a simple method for synthesis of BiVO4 microcrystals as efficient electrode material for PEC water splitting.

Metal oxide-metal sulfide-based composites of desired properties are of great technological importance because of their applications ranging from photovoltaics to energy storage devices. Herein, we report on the structural and charge storage capabilities of nickel-doped zinc sulfide-decorated zinc oxide (Ni–ZnS/ZnO) composite prepared by wet chemical route. The synthesis of ZnO, Ni–ZnS, and Ni–ZnS/ZnO was performed at 80 °C in a single vessel which was followed by annealing at 300 °C for 1 h. Scanning electron microscopy (SEM) images indicated flower-like morphology of the ZnO decorated with Ni-doped ZnS (Ni–ZnS). The material exhibited characteristic X-ray diffraction (XRD) signals corresponding to ZnO and Ni–ZnS which confirmed the formation of a composite structure. Energy-dispersive X-ray analysis, UV–visible spectroscopy, and Fourier Transform Infrared (FTIR) spectroscopy measurements revealed the successful formation of Ni–ZnS/ZnO composites. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out to examine the energy storage capabilities of the synthesized Ni–ZnS/ZnO composite. The composite electrode demonstrated a specific capacitance of 354 F g−1 in 1 M KOH electrolyte which was higher than that of the Ni–ZnS (154.7 F g−1) and ZnO (132 F g−1). The enhanced capacitive performance of the composite is attributed to the low charge transfer resistance and high electrochemically active specific surface area (27.54 m2 g−1), as revealed by EIS results.

Using first-principles calculations based on density-functional theory we systematically investigate the effect of applied strain on the stability and on the electronic and magnetic properties of monolayer phosphorene with single-atom vacancy. We consider two types of single vacancies: the symmetric SV- 55 | 66 , which has a metallic and non-magnetic ground state, and the asymmetric SV- 5 | 9 , which is energetically more favorable and exhibits a semiconducting and magnetic character. Our results show that compressive strain up to 10%, both biaxial and uniaxial along the zigzag direction, reduces the formation energy of both single-atom vacancies with respect to the pristine configuration and can stabilize these defects in phosphorene. We found that the magnetic moment of the SV- 5 | 9 system is robust under uniaxial strain in the range of −10 to +10%, and it is only destroyed under biaxial compressive strain larger than 8%, when the system also suffers a semiconductor-to-metal transition. Additionally, we found that magnetism can be induced in the SV- 55 | 66 system under uniaxial compressive strain larger than 4% along the zigzag direction and under biaxial tensile strain larger than 6%. Our findings of small formation energies and non-zero magnetic moments for both SV- 5 | 9 and SV- 55 | 66 systems under zigzag uniaxial compressive strain larger than 4% strongly suggest that a magnetic configuration in monolayer phosphorene can be easily realized by single-vacancy formation under uniaxial compressive strain.

Polyaniline/Poly(o-aminophenol) (PANI/POAP) bilayered films were deposited by electro polymerization on platinum (Pt) and graphite (Gra) electrodes for methanol oxidation in direct methanol fuel cells. The chemical composition of bilayered structure was characterized by Fourier transform infrared (FTIR) spectroscopy. Results demonstrated the presence of FTIR peaks associated to PANI and POAP constituents confirming the bonding of PANI and POAP in the bilayered composite structure. The electrochemical properties of PANI/POAP electrodes were examined in pure and sulfuric acid mixed methanol solutions using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). PANI/POAP-Gra electrode showed less reactivity towards methanol oxidation, as well as poor stability upon repeated cycling. On the other hand, PANI/POAP-Pt electrode exhibited superior performance with high methanol oxidation current (Ia), capacitance (C), and specific capacitance (Cs). In addition, PANI-POAP-Pt electrode was found better than PANI-POAP-Gra electrode in terms of operation stability based on continuous cycling in methanol up to 100 cycles. The dielectric properties and AC conductivity (σac) of the PANI/POAP-Pt electrode with respect to the applied potential have been discussed.

In this study, a simple and cost-effective chemical bath deposition was employed to deposit nan-sized hematite (α-Fe2O3) directly on fluorine-doped tin oxide (FTO) substrates. The structure, morphology, and optical properties of α-Fe2O3 were manipulated by adjusting the experimental parameters, particularly the deposition temperature and precursor concentration. With increase in Fe precursor concentration from 0.1 M to 0.3 M, the surface morphology was changed from granular-shape condensed particles to vertically aligned rod-like structures. XRD spectra indicated signals from FTO substrate and pure α-Fe2O3 phase which corresponds to the rhombohedral system. The XPS analysis revealed the presence of α-Fe2O3 in the film and no tin (Sn) impurities from the FTO substrate. By changing the deposition temperature from 60 ℃ to 90 ℃, the size of particles increased; whereas, the surface morphology was not altered. The resultant films were examined as photoanode for photoelectrochemical (PEC) water splitting. The optimized electrode exhibited maximum water splitting photocurrent density of 700 μA.cm−2 at 1.6 V versus reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5, 100 mW.cm−2) in 1 M NaOH. This could be attributed to the large electrode electrolyte interfacial area and low charge transfer resistance offered by nanorods of α-Fe2O3 of high surface-to-volume ratio.

For the first time, bismuth oxide (Bi 2 O 3 ) nanoplates synthesized by single-step chemical method were envisaged as photoanodes in dye-sensitized solar cells. The structural elucidation demonstrated tetragonal structure with a predominant β-Bi 2 O 3 . The power conversion efficiency (1%) of Bi 2 O 3 nanoplates-based dye-sensitized solar cells was enhanced up to 50% when decorated with zinc oxide thin layer (ZnO). The best performing electrode showed 24% incident photon-to-current conversion efficiency. This high DSSC performance of Bi 2 O 3 –ZnO photoanode is attributed to the increased electron transportation due to the suppression of recombination centers by ZnO passivation layer.

Electrochemically deposited α-Fe2O3 thin films, whose composition was tuned by Pt doping, were investigated as photoanode for photoelectrochemical water splitting. Morphological and structural characteristics of the nanostructured α-Fe2O3 thin films were studied by scanning electron microscopy and X-ray diffraction techniques. The films were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy to determine the effect of Pt doping on the α-Fe2O3 structure. The photoelectrochemical performance of the films was examined by linear sweep voltammetry and electrochemical impedance spectroscopy. Results of these studies showed that Pt doping increased the density of small-sized nanoparticles in α-Fe2O3 thin films. The Pt doped films exhibited higher photoelectrochemical activity by a factor of 1.4 over un-doped α-Fe2O3 films. The highest photocurrent density of 0.56 mA cm−2 was registered for 3% pt doped film at 0.4 V versus Ag/AgCl in 1 M NaOH electrolyte and under standard illumination conditions (AM 1.5 G, 100 mW cm−2). This high photoactivity can be attributed to the high active surface area and increased donor density caused by Pt doping in the film. Electrochemical impedance analysis also revealed significantly low charge transfer resistance of Pt doped films, indicating its superior electrocatalytic activity for water splitting reaction compared to un-doped α-Fe2O3 thin films.

In this study, nanostructured α-Fe 2 O 3 thin films were deposited by simple electrodeposition for photoelectrochemical water splitting. Post-annealing temperature was found to have drastic effect on photoactivity of these films. SEM analysis illustrated that size of nanoparticles increases with annealing temperature. The current–potential characteristics showed that the water-splitting photocurrent strongly depends on post-annealing temperature. A maximum photocurrent density of 0.67 mA/cm 2 was observed at 1.23 V versus reversible hydrogen electrode (RHE) under standard illumination conditions (AM 1.5 G 100 mW/cm 2 ), and the water-splitting current was over 1.0 mA/cm 2 before the dark current flow starts (at 1.55 V versus RHE). The electrode shows an onset potential as low as 0.8 V (versus RHE) for water photooxidation, which is one of the best results reported for hematite photoanodes. This high photoactivity of electrodes is attributed to the preferential growth of hematite nanostructures along the most conductive plane (001) and incorporation of Sn in film from the substrate at high annealing temperature. The best-performing electrode shows an incident photon conversion efficiency (IPCE) of 12% at 400 nm (in 1 M NaOH at 1.23 V versus RHE), which indicate the improved light-harvesting properties of these nanostructures.

Nanostructured iron oxide thin films have been prepared by electrodeposition technique and annealed at various temperatures. The effect of deposition potential, deposition time and annealing temperature on photoelectrochemical (PEC) properties of α-Fe 2 O 3 thin films was studied. The (1 0 4) and (1 1 0) peak presence in X-ray diffraction patterns confirms α-Fe 2 O 3 phase formation. The transition on surface morphology from nanosheets to elongated dumbbell shaped nanoparticles occurred that can be attributed to annealing temperature varied from 400 to 700 °C. Optical band gap variation was observed due to annealing temperature. It was found that increment in film thickness increases the photocurrent from 253 μA/cm 2 to 488 μA/cm 2 at 0.4 V vs Ag/AgCl.

Based on results of density functional theory (DFT) calculations with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), we propose a new magnetic material, CsCl-type FeSe. The calculations reveal the existence of ferromagnetic (FM) and antiferromagnetic (AFM) states over a wide range of lattice constants. At 3.12\,{\AA} in the GGA, the equilibrium state is found to be AFM with a local Fe magnetic moment of $\pm 2.69\,\mu_\mathrm{B}$. A metastable FM state with Fe and Se local magnetic moments of $2.00\,\mu_\mathrm{B}$ and $-0.032\,\mu_\mathrm{B}$, respectively, lies 171.7\,{meV} above the AFM state. Its equilibrium lattice constant is $\sim 2$\,{\%} smaller than that of the AFM state, implying that when the system undergoes a phase transition from the AFM state to the FM one, the transition is accompanied by volume contraction. Such an AFM-FM transition is attributed to spin-density $z$-reflection symmetry; the symmetry driven AFM-FM transition is not altered by spin-orbit coupling. The relative stability of different magnetic phases is discussed in terms of the local density of states. We find that CsCl-type FeSe is mechanically stable, but the magnetic states are expected to be brittle., Comment: LaTeX,16 pages, 6 figures

Magnetic and electronic structure calculations are performed for Mn 2 As with antiferromagnetic (AFM), ferromagnetic (FM), and ferrimagnetic (FIM) spin ordering, using the full-potential linearized augmented plane-wave (FLAPW) method based on the generalized gradient approximation (GGA). It is shown that AFM is the magnetic ground state of Mn 2 As, which is in agreement with the experimental observations. At a low temperature (0 K), AFM–FIM transition is also predicted which is consistent with the previous predictions. The ground state stability of the magnetic structure of Mn 2 As is attributed to the nearest Mn (I) and Mn (II) antiferromagnetic interaction. The calculated magnetic moment of Mn (II) 3.44 μ B is found to be in good agreement with the neutron diffraction experiment 3.50 μ B while there is a disagreement for the magnetic moment of Mn (I). The different magnetic moments are reflected in the electronic structures of Mn 2 As and the exchange splitting between Mn atoms is shown to be an intra-atomic effect.

The spin-polarized full potential linearized augmented plane wave (FLAPW) method in the generalized gradient approximation (GGA) is carried out for investigation on the magnetism of the zinc-blende CrP(0 0 1) surface. We found that the Cr-terminated surface retains the half-metallic character, while the half-metallicity is destroyed for the P-terminated surface due to surface states, which originate from p electrons. The magnetic moment of Cr at the surface (sub-surface) is found to be enhanced (reduced) compared to that of the bulk-like Cr atom.

Magnetic and electronic structure calculations are carried out for hypothetical zinc-blende (zb) phase of FeX (X=P, As, Sb) by using the full-potential linearized augmented plane wave (FLAPW) method. For zb FeSb, the total energy has been calculated as a function of lattice constant in ferromagnetic (FM) and antiferromagnetic (AFM) states. We found that the ground state of zb FeSb is very stable with respect to compression and expansion of the unit cell. The magnetic moment of zb FeSb in the AFM state is increasing with the lattice constant. The magnetic and electronic structures calculations of FeAs (FeP) are carried out for the lattice constants of GaAs (GaP), InAs (InP), and Si. Our finding shows that AFM is the ground state for all of our calculated zb FeX compounds and do not belong to the class of zb half metallic ferromagnets.