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We investigated the electronic structure modifications in two-dimensional (2D) pentagonal PdS2 materials by external strains. In the absence of external strain, the 2D pentagonal PdS2 materials are indirect band gap semiconductors. The band gap decreases with an increase in the number of stacking PdS2 monolayers. The external uniaxial and biaxial strains significantly modify the contributions of p-orbitals of S atoms and d-orbitals of Pd atoms to the conduction and valence band edges. It consequently modifies the electronic structures of 2D pentagonal PdS2 materials. This strain tunability of electronic structures of 2D pentagonal PdS2 materials may be useful for their electro-mechanical applications. [ABSTRACT FROM AUTHOR]

The substitutional doping of graphene and related materials with Boron (B) and/or Nitrogen (N) atoms can be effectively used to tailor their properties for specific applications. In this paper, we investigate the energetics, electronic structures and vibrational spectra of substitutional pair-defects in graphene and graphane. The structural distortions in the vicinity of BN pair-defects are small as compared to the distortions in the vicinity of BB or NN pair-defects. The BB (NN) pair-defects in graphene and graphane transform them into p (n) semiconductors. However, the BN pair-defects doped graphene and graphane are intrinsic semiconductors. The Raman and IR spectra of above mentioned pair-defects have unique features, which can be used to identify these defects in graphene as well as graphane structures. [Display omitted] • Substitutional pair-defects doped in graphene and graphane show their signatures in electronic and optical properties. • BB (NN) pair-defects in graphene and graphane transform them into p(n) type semiconductors. • Raman and IR spectra of pair-defects have unique features, which can be used to identify these defects in graphene as well as graphane structures. [ABSTRACT FROM AUTHOR]

We compute the temperature dependent relaxation time (τ) of charge carriers in LiScX (X = C, Si, Ge) half-Heusler (hH) alloys using the deformation potential theory. This temperature dependent τ of charge carriers is used to investigate its effect on the thermoelectric properties of these hH alloys. It is shown that there is a significant effect of temperature dependent τ of charge carriers on the thermoelectric properties of these hH alloys. • Temperature dependent relaxation time considered for calculating electrical conductivity • Comparison done with constant relaxation time results also. • Results are more practical as thermal conductivity computed using Callaway model and Slack equation. Both are found to be in excellent agreement. • Thermodynamic parameters calculated and stability has been established. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots (QDs) have been extensively investigated for potential applications such as on-demand sources of triggered single photons and entangled photon pairs. One of the methods to generate polarization-entangled photon pairs using the QDs requires vanishing fine structure splitting (FSS) of exciton emission, while another method involves the time-resolved tomographic measurements of the polarization state of pairs of photons emitted during the radiative cascade of the confined biexciton in a semiconductor QD. Efficient use of these methods requires the tuning of exciton emission energy or FSS in QDs. There has been a great progress in last decade to tune FSS and exciton emission energy. In this paper, we present a brief review of the tuning of FSS and exciton emission energies in semiconductor QDs. We present the effect of different structural parameters and external perturbations on the FSS and exciton emission energy of QDs. [ABSTRACT FROM AUTHOR]

The spin-orbit splitting ( E) of valence band maximum at the point is significantly smaller in 2D planner honeycomb structures of graphene, silicene, germanene and BN than that in the corresponding 3D bulk counterparts. For 2D planner honeycomb structure of SiC, it is almost same as that for 3D bulk cubic SiC. The bandgap which opens at the K and K points due to spin-orbit coupling (SOC) is very small in flat honeycomb structures of graphene and silicene, while in germanene it is about 2 meV. The buckling in these structures of graphene, silicene and germanene increases the bandgap opened at the K and K points due to SOC quadratically, while the E of valence band maximum at the point decreases quadratically with an increase in the magnitude of buckling. [ABSTRACT FROM AUTHOR]

We present an accurate computational study of the electronic structure and lattice dynamics of solid molecular hydrogen at high pressure. The band-gap energies of the [ABSTRACT FROM AUTHOR]

We study the potential energy surface (PES) of the ozone molecule along the normal modes by means of Quantum Monte Carlo simulations based on the resonating valence bond concept. The trial wave function consists of an antisymmetrized geminal power arranged in a single determinant that is multiplied by a Jastrow correlation factor. Whereas the determinantal part incorporates static correlation effects, the augmented real-space correlation factor accounts for the dynamics electron correlation. The accuracy of this approach is demonstrated by computing the dissociation energy and PES for the ozone molecule in three vibrational states: symmetric, asymmetric, and scissoring. We find that the employed wave function provides a detailed description of rather strongly correlated multireference systems, which is in quantitative agreement with experiment, using a single determinant only. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We present theoretical calculations of the Raman and IR spectra, as well as electronic properties at zero and finite temperature to elucidate the crystal structure of phase III of solid molecular hydrogen. We find that anharmonic finite temperature are particularly important and qualitatively influences the main conclusions. While P63/m is the most likely candidate for phase III at the nuclear ground state, at finite temperature the C2/c structure appears to be more suitable. [ABSTRACT FROM AUTHOR]

Abstract: Conventional magnetic order in a material requires the partially filled d or f bands. The exchange interactions between the electrons in these partially filled bands give rise to a magnetic order. However, the discovery of unexpected magnetism observed in some nanomaterials, which have the d and f shells either completely empty or full, has challenged our understanding of magnetism in conventional materials. The magnetism in nanomaterials shows the effects of reduced dimensions, reduced coordination of atoms at the surface and some quantum effects which dominate at low dimensions. In this review paper we give a brief review and discuss the unexpected magnetism experimentally observed and/or theoretically predicted in nanomaterials of conventional magnetic and nonmagnetic bulk materials. [Copyright &y& Elsevier]

We investigate strained InxGa1−xAs/GaAs and strain-free GaAs/Al0.3Ga0.7As quantum dots (QDs) grown on (110)-oriented substrates by means of atomic empirical pseudopotentials and configuration interaction. We find that there is a significant piezoelectric effect on the exciton fine structure splitting (FSS) in strained QDs due to the in-plane character of the electric field. The ground-state bright excitons in these QDs are polarized along the [001] and [1̅ 10] crystal directions, and have large FSSs. The linear degree of polarization is large and decreases linearly with an increase in Ga content, while it is nearly zero and independent of Ga content in InxGa1−xAs/GaAs QDs with similar shape and size grown on (001) substrates. [ABSTRACT FROM AUTHOR]

We investigate the vertical electric field tuning of the exciton fine-structure splitting (FSS) in several InGaAs and GaAs quantum dots (QDs) using the atomistic empirical pseudopotential approach and configuration interaction. We find that the FSS is surprisingly tunable, with a rate similar to the one reported for lateral electric fields. The minimum FSS for GaAs QDs often lies below the radiative linewidth, which makes them good candidates for the generation of entangled photon pairs. We highlight, however, that random alloy fluctuations affect the minimum FSS by ± 1.4µeV, so that a postselection of QDs may still be beneficial to obtain entangled photon pairs with the highest fidelity. We suggest a simple experimental procedure for this task. The FSS is therefore a rare observable, where the specific decoration of the random alloy lattice matters significantly. [ABSTRACT FROM AUTHOR]

We study the effect of atomic ordering on the electronic and optical properties of InGaAs/GaAs semiconductor nanostructures via atomistic empirical pseudopotentials. We find that ordering sharply increases the polarization anisotropy and the fine structure splittings, and we explain the underlying physics. We suggest that ordering may be responsible for some experimental results where large values of these observables have been reported. We show that ordering pins the polarization into a certain direction that remains robust upon elongation of the structure--a fact that may be advantageous for use as polarized light sources. [ABSTRACT FROM AUTHOR]

We suggest theoretically the existence of a stoichiometric derivative of graphene, a two-dimensional analog of polyvinylidene fluoride, with fluorine and hydrogen atoms alternately attached to carbon atoms in a chairlike configuration. Analyzing the different possible decorations of H and F of graphene, we find that all are unstable but one. This low-energy structure has a wide band gap and an elastic strength comparable to that of pristine graphene. One other structure is shown to become stable under compressive stress. [ABSTRACT FROM AUTHOR]

We report the first-principle calculations of ferromagnetism in C-doped ZnO clusters. The carbon impurities in ZnO clusters are doped at substitutional O or Zn sites and at interstitial sites and the total energy calculations suggest C at O site is more stable than that at Zn site. The substitutional C impurity is found more favorable than interstitial C impurity in these clusters. The ZnC region is mainly responsible for the observed ferromagnetism in ZnO:C systems. The average magnetic moment of ZnnOn-mCm clusters is found to be 2 μB/C for n, m < 7. For n, m > 6 the magnetic moment decreases below 2 μB/C. The magnetic moment in (ZnO)nCi; i = 1 - 2 is found to be 0.1-2.0 μB/C. The combination of substitutional and interstitial C impurities in ZnO clusters leads to magnetic moment of 0.4-1.0 μB/C. [ABSTRACT FROM AUTHOR]

Abstract: We investigated structural optimization of stage-1 binary graphite 3d-transition metal intercalated compounds (XC6; X=Cr, Mn, Fe) using the spin-polarized density functional theory. Total energy calculations show that CrC6 and FeC6 prefer rhombohedral (R-3m) crystalline structures, while MnC6 prefer hexagonal (P63/mmc) crystalline structure. The ground state structures of CrC6, MnC6 and FeC6 are metallic. The magnetic moments of ground state structures of MnC6 and FeC6 are 1.01 and 1.70μB respectively, while that of CrC6 is nearly zero. [Copyright &y& Elsevier]

The magnetic coupling in pseudomorphic overlayer and sandwich structures of 2ML magnetic ultrathin films on Cu(001) substrate is investigated by using spin-polarized density functional theory. The 2ML magnetic overlayers have significant magnetic moment except CrNi overlayer for which magnetic moment is very small (0.004 μB/atom). The overlayers having one layer of Cr turn out to be antiferromagnetically coupled except CrNi/Cu overlayer which has ferromagnetic coupling. All other overlayers have ferromagnetic coupling. In contrast to ferromagnetic MnMn/Cu overlayer, the Cu/MnMn/Cu sandwich has antiferromagnetic coupling. Similar to CrFe/Cu overlayer, the Cu/CrFe/Cu sandwich has antiferromagnetic coupling, while all other sandwiches have ferromagnetic coupling. The sandwiched structures have reduced magnetic moment as compared to their overlayer counterparts. The MnMn, MnFe, and MnCo sandwiches have highly reduced magnetic moment as compared to their overlayer counterparts. [ABSTRACT FROM AUTHOR]

Abstract: The local magnetic structures around substitutional 3d transition metal impurities at cation sites in zinc blende structures of III–V (GaN, GaAs) and II–VI (ZnTe) semiconductors are investigated by using a spin-polarized density functional theory. We find that Cr-, Co-, Cu-doped GaN, Cr-, Mn-doped GaAs and Cr-, Fe-, Ni-doped ZnTe are half metallic with 100% spin polarization. The magnetic moments due to these 3d transition metal (TM) ions are delocalized quite significantly on the surrounding ions of host semiconductors. These doped TM ions have long range interactions mediated through the induced magnetic moments in anions and cations of host semiconductors. For low impurity concentrations Mn in GaAs also has zero magnetic moment state due to Jahn–Teller structural distortions. Based upon half metallic character and delocalization of magnetic moments in the anions and cations of host semiconductors these above mentioned 3d TM-doped GaN, GaAs and ZnTe seem to be good candidates for spintronic applications. [Copyright &y& Elsevier]

The fullerene cage clusters C60 and C70 become magnetic and half metallic when doped with B and N atoms. The five-atom transition metal clusters of Mn, Fe, Co, and Ni encapsulated inside fullerene cages have higher magnetic moment, while that of Cr become nonmagnetic as compared to corresponding isolated clusters. These clusters encapsulated inside fullerene cages get distorted. The distortion in a cluster inside C70 is larger as compared to that inside C60, C59B, and C59N cages. These clusters also distort the hexagons and pentagons of fullerene cages. The fullerene cages expand but retain their shapes. The energy calculations show that Mn and Cr clusters encapsulated inside C60 and C59N are stable. [ABSTRACT FROM AUTHOR]

Abstract: Pseudomorphic ultrathin (1–4 ML) free standing films, overlayers, and sandwiches of Cr, Mn, Fe, Co and Ni on fcc-Cu are investigated using spin-polarized ab-initio calculations. All free standing thin films have quite high magnetic moment, with the exception of the 2 ML Mn film which has zero magnetic moment. Sandwiches show the same magnetic behavior as overlayers, but with reduced magnetic moments. The 3 ML overlayer of Fe has a different structure than any other overlayer structure. Sandwiches built of monolayers of Ni and Cr in Cu have zero magnetic moment. The ultrathin free standing films, overlayers and sandwiches of Cr, Mn and Fe exhibit an oscillating magnetic moment depending upon the number of layers. We attribute this to alternating ferromagnetic and antiferromagnetic coupling. On the contrary, thin films of Co and Ni always show a ferromagnetic coupling, with a magnetic moment per atom converging towards a constant value. The magnetic moment induced in Cu atoms at the interface is significant for Mn, Fe, and Co (0.02–), while it is zero for the Ni/Cu interface. [Copyright &y& Elsevier]

The structural properties of amorphous silicon models generated with Reverse Monte-Carlo Modeling techniques are presented. The structure factors and radial distribution functions of the generated models closely resemble with the experimental data, but show some dependence on the sample size. However, the coordination defects show no direct correlation with the size of the sample. There exists no peak at 60° in the Si–i–Si bond angle distributions in these samples. The Si–Si–Si bond angle distributions in these samples are quite in good agreement with the Monte-Carlo and Molecular Dynamics simulations data. [ABSTRACT FROM AUTHOR]

The average function (average of sine and Gaussian functions) is used to investigate the vibrational properties of spherical semiconductor nanocrystals within the framework of phenomenological phonon confinement model [Solid State Commun. 39 (1981) 625]. The results for the phonon confinement and Raman intensity peaks are quite in agreement with the microscopic calculations. It is proposed here that the average function should be used as a phonon weighting function for the spherical nanocrystals, if the phonon confinement model [Solid State Commun. 39 (1981) 625] is being used to investigate their vibrational properties. [Copyright &y& Elsevier]

The enhancement in the phonon DOS of nanocrystalline fcc Ni at low and high energies is due to the anisotropic changes in the interatomic force constants as compared to the bulk phase fcc Ni. The specific heat and vibrational entropy of nanophase is found to be greater than that of the bulk phase. There occurred a peak in the excessive specific heat of nanocrystalline fcc Ni at low temperatures. The excessive entropy of nanocrystalline Ni also has a peak at low temperatures but it becomes constant at high temperatures. The free energy of nanophase is lower than that of the bulk phase. The difference in the free energies of bulk phase and nanophase Ni increases linearly with temperature. [Copyright &y& Elsevier]

We investigate the effect of nuclear quantum effects in liquid hydrogen at the thermodynamic conditions of room temperature and a pressure of 490 GPa. The calculated pair-correlation function shows that the nuclear quantum effects are quite significant for the correct description of liquid atomic hydrogen at high pressures. [ABSTRACT FROM AUTHOR]

We investigate the effect of full hydrogenation and fluorination on the spin-orbit coupling (SOC) in graphene, silicene and germanene. In chair conformation, the fluorination of graphene increases the spin-orbit splitting (Eso), while the hydrogenation and fluorination of other structures reduce the Eso at the Γ-point. In case of boat conformation, the hydrogenation and fluorination reduce the symmetry of honeycomb structure, which in turn remove the degeneracy of valence band maximum at the Γ-point. The change in band gaps due to SOC is very small in boat conformation structures as compared to that in the corresponding chair conformation structures. [ABSTRACT FROM AUTHOR]

Review: 294 refs. [ABSTRACT FROM AUTHOR]

We investigate the effects of point charge defects on the single-particle electronic structure, emission energies, fine structure splitting, and oscillator strengths of excitonic transitions in strained In0.6Ga0.4As/GaAs and strain-free GaAs/Al0.3Ga0.7As quantum dots. We find that the charged defects significantly modify the single-particle electronic structure and excitonic spectra in both strained and strain-free structures. However, the excitonic fine structure splitting, polarization anisotropy, and polarization direction in strained quantum dots remain nearly unaffected, while significant changes are observed for strain-free quantum dots. [ABSTRACT FROM AUTHOR]

Native defects are present in materials under various growth conditions. A fundamental understanding of the effect and nature of these defects in the lattice is crucial to optimize its thermoelectric performance. In this paper, we investigate the influence of the vacancy defects on the thermoelectric performance of the SnSe sheet. The results indicate that the process of vacancy formation is endothermic in nature. The calculated electronic structure shows that the band gap in case of sheet containing one Se vacancy decreases whereas the band gap in case of sheet containing a pair of Sn & Se vacancies increases with respect to the pristine sheet. However, in case of the sheet containing one Sn vacancy, the formation of a lone pair state near the valance band maximum results in the disappearance of band gap in the sheet. The calculated relaxation time of charge carriers shows higher values for the pristine sheet as compared to the sheet containing vacancies. The transport calculations show that the introduction of vacancies in the lattice deteriorates the thermoelectric performance of the sheet. • Systematic investigations of influence of vacancies on the thermoelectric properties has been performed. • Introduction of vacancies in the sheet results in dangling states formation in the gap region between VBM and CBM. • The bandgap for sheet containing Se vacancy decreases whereas bandgap for sheet containing a pair of Se & Sn vacancies increases w.r.t. pristine sheet. • In case of Sn vacancy, the bandgap of the sheet is disappeared due to formation of dangling states. • The transport coefficients of the sheet are deteriorated with the introduction of vacancies in the sheet. [ABSTRACT FROM AUTHOR]

• Energy band gap increases in case of isotropic tensile strain whereas it decreases in case of compressive strain. • Lattice thermal conductivity increases when tensile strain is applied. • Lattice thermal conductivity decreases in case of isotropic compressive strain. • increase in tensile strain leads to an overall increase in ZT values of n-type LiScGe. • increase in compressive strain increases ZT of p-type LiScGe. In the present work, we investigated the effect of isotropic strain, both tensile (up to 9%) and compressive (up to − 9%) on the electronic structure and transport properties of LiScGe half-Heusler (hH) alloy. The electronic structure calculations using the density functional theory reveal that increase in tensile strain widens the energy band gap, whereas increase in compressive strain shortens it. It is found that lattice thermal conductivity (k l) calculated using both the Slack's equation and Callaway Model increases with increase in tensile strain in general whereas in case of compressive strain, k l decreases as strain is increased. Our results for transport properties show that increase in tensile strain leads to an overall increase in ZT values of n-type LiScGe and increase in compressive strain increases ZT of p-type LiScGe. ga1 In the present work, we investigated the effect of isotropic strain, both tensile (up to 9%) and compressive (up to − 9%) on the electronic structure and transport properties of LiScGe half-Heusler (hH) alloy. The electronic structure calculations using the density functional theory reveal that increase in tensile strain widens the energy band gap, whereas increase in compressive strain shortens it. The electronic thermal conductivity, κ e = κ 0- S 2 σT (where κ 0 is the short-circuit electronic thermal conductivity) decreases under tensile strain whereas it increases under compressive strain with S 2 σT term playing a significant role in the determination of κ e. The bipolar contribution to thermal conductivity (κ bp) is found to decrease under tensile strain while it increases in case of compressive strain at strain values higher than − 3%. It is found that lattice thermal conductivity (κ l) calculated using both the Slack ′ s equation and Callaway Model increases with increase in tensile strain in general whereas in case of compressive strain, κ l decreases as strain is increased. Our results for transport properties show that increase in tensile strain leads to an overall increase in ZT values of n -type LiScGe and increase in compressive strain increases ZT of p -type LiScGe. [ABSTRACT FROM AUTHOR]

• The thermoelectric properties of bilayer SnSe are still not explored yet experimentally and theoretically. • The lattice thermal conductivity of bilayer SnSe is ultralow (0.90 Wm−1 K−1) at room temperature. • Temperature dependent relaxation time has been used to calculate the thermoelectric properties of bilayer SnSe. • The peak value of ZT is 0.72 (0.78) along zigzag (armchair) direction. The low-temperature bulk phase of SnSe has a layered structure with AB-type of stacking of two-atom-thick SnSe monolayers. However, in the case of bilayers the AA-stacked SnSe bilayer structure is most stable. Similar to bulk SnSe, AA-stacked SnSe bilayer has ultralow lattice thermal conductivity of 0.90 Wm−1 K−1 at room temperature which is quite low as compared to other two dimensional materials. Our results show that n -type SnSe bilayer has good thermoelectric performance as compared to that of the p -type bilayer. [ABSTRACT FROM AUTHOR]

We explore the effect of hydrostatic pressure on the transport properties of L i S c G e half-Heusler compound upto 50 G P a using the Density functional theory (D F T) and the semi-classical Boltzmann transport theory. Our results show that for n -type doping, thermoelectric performance of L i S c G e decreases with increase in pressure. However, for p -type material thermoelectric performance decreases upto 10 G P a , and then it increases with increase in pressure. We explore the effect of hydrostatic pressure on the transport properties of LiScGe half-Heusler compound. We perform calculations upto 50 GPa using the density functional theory (DFT) and the semi-classical Boltzmann transport theory. Our results show that for n-type doping, thermoelectric performance of LiScGe decreases with increase in pressure. However, for p-type material the thermoelectric performance decreaeses upto 10 GPa and then it increases with increase in pressure. A maximum value of ZT = 0.77 is obtained in p-type LiScGe at 50 GPa and 700 K.Figure: The variation of figure of merit (ZT) for n-type and p-type LiScGe as a function of temperature at different pressures. Image 1 • The effect of hydrostatic pressure on the transport properties of LiScGe half-Heusler compound is investigated. • For n-type doping, thermoelectric performance decreases with increase in pressure. • For p-type doping, ZT first decreases up to 10 GPa and afterwards it increases with increase in pressure. • A maximum value of ZT = 0.77 is obtained in p-type LiScGe at 50 GPa and 700 K. [ABSTRACT FROM AUTHOR]

Abstract: Three samples of amorphous TiO2 of 3nm size are prepared by molecular dynamics simulations using different heating and quenching rates and open boundary conditions. Matsui–Akaogi force field is used to calculate the correlation functions. It is found that atomic distribution in these samples differ within the limit of 4%. The calculated coordination numbers suggest that 52–54% Ti atoms are 6-fold coordinated, 31–32% Ti atoms are 5-fold coordinated, 7–10% are 4-fold coordinated and few Ti atoms even 7-fold coordinated through vertex and edge sharing in these samples. On the other hand 66–68% oxygen atoms remain 3-fold coordinated, 25–28% are 2-fold coordinated and 5–6% oxygen atoms become 4-fold coordinated. Most of the over coordinated and under coordinated strained structures are in the core and surface regions respectively. The agreement between the calculated and measured reduced structure factors suggests that atomic arrangements in the laboratory samples prepared by sputtering and sol-gel methods may be similar to those predicted by molecular dynamics simulations. [Copyright &y& Elsevier]

High resolution X-ray diffraction (HRXRD) pattern of highly c-oriented (002) thin film provide a direct evidence of the formation of R-3c orthorhombic ZnCO 3 structural phase. Room temperature ferromagnetism (RTFM) is measured using bulk vibrating sample magnetometery (VSM). A strong orbital anisotropy has been observed by X-ray linear dichroism (XLD) experiment, which also supports that ZnCO 3 phase is structurally non-distortive after carbon-implantation. The absence of X-ray magnetic circular dichroism (XMCD) signal at O K- and C K-edges suggest that bulk VSM ferromagnetism is not related to the magnetic polarization of O 2 p /C 2 p orbitals hybridized with Zn-states. These experiments clearly indicate that the complex C–ZnO/ZnCO 3 phase should be ferromagnetic having out-of-plane/in-plane orbital reconstruction. • Structural, and electronic/magnetic properties of Carbon implanted ZnO thin films. • Observation of C–ZnO/ZnCO 3 complex responsible for ferromagnetism having out-of-plane/in-plane orbital. • VSM ferromagnetism is not related to the magnetic polarization of O 2p/C 2p orbitals hybridized with Zn-states. [ABSTRACT FROM AUTHOR]