Energy Density Of States Research Articles

The Effect of Electric Field on Carrier Mobility in Organic Semiconductors Based on Exponential Type Density of States and Genuine Transport Energy

Carrier mobility plays a crucial role in organic semiconductors because it limits the efficiency of organic devices. Based on the exponential type density of states (EC DOS) and genuine transport energy, we introduce a model to describe the dependence of electric field and carrier mobility in organic semiconductors by using effective medium approximation. The theoretical results show that the carrier concentration is a key factor to influence the carrier mobility, which increases with the increasing carrier concentration. The Poole-Frenkel behavior is reproduced in our model. The calculated carrier mobility as functions of electric field at different temperatures are in good agreement with analytical data for 40’-(3,7-dimethyloctyloxy)-1,1’-biphenylene-2, 5-vinylene] (NRS-PPV).

Path integral Monte Carlo method for the quantum anharmonic oscillator

The Markov chain Monte Carlo (MCMC) method is used to evaluate the imaginary-time path integral of a quantum oscillator with a potential that includes a quadratic term and a quartic term whose coupling is varied by several orders of magnitude. This path integral is discretized on a time lattice on which calculations for the energy and probability density of the ground state and energies of the first few excited states are carried out on lattices with decreasing spacing to estimate these quantities in the continuum limit. The variation of the quartic coupling constant produces corresponding variations in the optimum simulation parameters for the MCMC method and in the statistical uncertainty for a fixed number of paths used for measurement. The energies and probability densities are in excellent agreement with those obtained from numerical solutions of Schrödinger’s equation. The theoretical and computational framework presented here introduces undergraduates to the path integral formulations of quantum mechanics in real time and the partition function in statistical mechanics in imaginary time. The example of the anharmonic oscillator helps to build an intuition about the MCMC method of evaluating the partition function, which can then be used to solve other problems in physics and beyond.

Ab Initio and Experimental Study of Electronic, Optical, and Vibrational Properties of CdGa2Te4

The electronic, optical, and lattice oscillatory properties of CdGa2Te4 have been studied experimentally using spectral ellipsometry, Raman scattering (R) and infrared (IR) spectroscopy, as well as theoretically using the density functional theory (DFT). Eight Raman-active modes and twelve IR-active modes are detected and identified from consideration of the point symmetry group. Based on the analysis of the electronic spectrum and the density of energy states, the nature of the chemical bond in this semiconductor compound is determined. The theoretically calculated results are compared with the experimental data of the present work and with the results of experimental data available in the literature obtained by infrared spectroscopy and Raman scattering.

Density functional theory study of perfluorooctane sulfonate adsorption on fluorinated graphene

Density functional theory calculations are carried out to explore the adsorption behaviour of perfluorooctane sulfonate (PFOS) on pristine and fluorinated graphene. Then, the effects of different degrees of fluorination of graphene on the adsorption of PFOS are systematically investigated by analysis of the adsorption energy (E ads), electron transfer and partial density of states. Finally, the unique adsorption behaviour of PFOS on graphene and fluorinated graphene is demonstrated by a companion study of four other organic molecules, namely hepta-fluorobutyric acid, phenanthrene, phenol and perfluorooctanoate.

Designing biotechnological processes to reduce emulsions formation and improve oil recovery: Study of antifoams application

Fermentation aiming at oil production has emerged as an outstanding technique, but an undesirable emulsion can be formed preventing oil separation. There is still little knowledge about the mechanisms triggering the formation of such emulsions. Although this phenomenon is partly attributed to the cells presence, other essential compounds can contribute to the stability of emulsions, due to their surface properties. Thus, this study aimed at investigating the mechanisms of emulsions stabilization by Saccharomyces cerevisiae (a model microorganism) and two well-known antifoaming agents (Pluronic L81 and Antifoam C), since the surface properties of antifoams have hitherto gathered limited attention. This study also simulated conditions of energy density within the range used in similar bioprocesses. Emulsions were evaluated from droplet size, rheological properties, optical and confocal microscopy. Albeit all emulsions were stable, Pluronic L81 led to a greater reduction in interfacial tension and droplet size values, showing the drawback of its application for product recovery. It was also observed that the molecular characteristics of oils can contribute to hinder oil recovery. Therefore, the choice of an antifoam depends on the properties of the oil to be recovered. Moreover, it was demonstrated that the set of methodologies used in this study can be a tool to study the colloidal effects of fermentation components to gain insights on the development of more feasible bioprocesses.

DFT study of the oxidation of Hg0 by O2 on an Mn-doped buckled g-C3N4 catalyst

Due to the water-insoluble nature of Hg0, its oxidization to Hg2+, which is water-soluble, is a viable approach for its effective removal at coal-fired plants using existing flue gas desulfurization (FGD) unit. In this study, the adsorption and oxidation of elemental mercury on an Mn-doped g-C3N4 material were investigated. The spin-polarized density functional theory method was adapted to optimize the geometry structures and then to determine the corresponding electronic structures, while the CI-NEB method was adopted to search for the stable intermediates during the reaction(s). The analysis of energy and project density of states shows that the Mn-g-C3N4 exhibits an excellent affinity to Hg atoms. It is found that it is feasible for Hg atoms to oxidize on the Mn-g-C3N4 surface via two possible E-R paths, but with relatively high energy barriers. This research provides insights into a viable way for mercury removal using O2 as the oxidizing agent.

Electronic and photocatalytic properties of Antimonene nanosheets

Electronic and photocatalytic properties of single-layer Antimonene nanosheets have been investigated. The variation of the energy gap between HOMO and LUMO levels concerning the nanosheet width along with both armchair and zigzag directions has been explored up to 388 atoms. It is shown that the armchair edges in Antimonene nanosheet are chemically more active than that of zigzag edge. Here, we also report that the Antimonene nanosheet can demonstrate photocatalytic properties for the whole range of pH. Besides, the density of energy states for these two frontier orbitals around the energy gap is reported. Interestingly, while the adiabatic electron affinity demonstrates a similar pattern for the two mentioned edges, the adiabatic ionization energy is mainly controlled by the length of the armchair edge. • Size-dependency of the Antimonene nanosheets for electronic and photocatalytic properties are presented. • Antimonene nanosheet can demonstrate photocatalytic properties for the whole range of pH. • The adiabatic ionization energy is mainly controlled by the length of the armchair edge. • The adiabatic electron affinity demonstrates a similar pattern for the two mentioned edges.

DFT COMPUTATION OF THE BAND STRUCTURE AND DENSITY OF STATE FOR ZnO HALITE STRUCTURE USING FHI-aims CODE.

This research work is on Density Functional Theory (DFT) within Local Density Approximation as parameterised by Perdew and Wang (pw-lda).The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHI-aims) code based on numerical atomic-centered orbital basis sets. The electronic band structure, density of state (DOS) and band gap energy were calculated for ZnO compound. The band structure and Density of States (DOS) diagrams are plotted from the calculated equilibrium lattice parameters. The experimentally lattice constant values were used to calculate the minimum total energy. The calculated electronic band structure results show that ZnO (Halite) is an indirect semiconductor with energy band gap of 0.89 eV. Hence, the HOMO is -0.863382 eV at L_symmetry point and LUMO is 0.0239417 eV at ᴦ- point. The DOS energy level within the compound shows considerable high state of electron occupation and the DOS observed around the Fermi level at zero level indicate that it has conducting properties. In general, FHI-aims code has shown better accuracy and prediction of band structure calculation within reasonable computational methods.

Tension and compression effect on mechanical properties of Fe and B2

The elastic constants, ideal strength, band structure and electronic density state of Fe and B2 under tension and compression were studied by using the first principle. The structural parameters calculated at 0 pressure are consistent with the experimental results. The dependence of elastic constant and stress can be obtained by using static finite strain technique. The ideal tensile and compressive strength of Fe and B2 were studied by calculating the stress-strain relationship. At last, the micro mechanism which affects the stability of the structure was analyzed by using the results of electronic structure calculation. The results show that the compressive strength of Fe and B2 structure is higher than the tensile strength. When the stress of cell structure exceeds a limit, it will be destroyed, resulting in the sudden decrease of Poisson’s ratio, B and G, the asymmetry of energy band structure and the decrease of electron density of state energy.

Interaction investigation of single and multiple carbon monoxide molecules with Fe-, Ru-, and Os-doped single-walled carbon nanotubes by DFT study: applications to gas adsorption and detection nanomaterials.

Due to the large surface area and unique electronic property, single-wall carbon nanotube (SWCNT) is being used for adsorption and detection nanomaterials, which can be used to reduce the CO pollution effect on the environment. In the present work, the adsorptions of single and multiple CO molecules on pristine and transition metal (TM = Fe-, Ru-, and Os)-doped SWCNT were investigated in terms of geometric, energetic, and electronic properties using density functional theory calculation. Calculated results display that the adsorption of CO molecule on the SWCNTs is energetically favorable. The TM-doped SWCNT are more highly interactive to CO adsorption than that of pristine SWCNT. An Os-doped SWCNT displays the strongest interaction with single and multiple CO molecules comparing with the Fe- and Ru-doped SWCNT. The TM doping on SWCNT can induce the charge transfer between CO molecule and the SWCNT. The energy gap and density of state are clearly changed when CO molecule interacts with TM-doped SWCNT, resulting in dramatic changes of their electronic properties. Therefore, TM-doped SWCNT are possibly used as potential CO storages/absorbents or sensor material for CO detection in the environment. Graphical abstract.

The strategy for improving the stability of nitroform derivatives-high-energetic oxidant based on hexanitroethane.

To develop high-energetic stability nitroform compounds, three types of nitroform derivatives based on hexanitroethane structure are designed. The guidelines for selecting these compounds are based on (1) constructing a flexible molecule and weakening the external force by elastic deformation and (2) forming negative ion or introducing electron-rich group to eliminate the electron-deficient situation. The conformations and some important properties of them are calculated at B3LYP/6-311 + G(d) level. Based on the bond order and bond dissociation enthalpy analysis, C-NO2 bond is considered to be the most unstable position, and both of the methods can improve the stability of designed compounds. Based on molecular energy gap (HOMO-LUMO) and density of state (DOS) analysis, it is found that introducing of bridge atoms is helpful to lower the sensitivity, while the construction of anions changes both HOMO-LUMO and DOS which shows obvious ionic properties. A further study on the electrical potential surface shows that the probability for extreme values of designed compounds decreases which is beneficial for high stability. Finally, the explosive properties and impact sensitivity of them are calculated. Results show that their explosive performances are obviously better than current energetic oxidants and some of them maintain low sensitivity.

DFT study of gas adsorbing and electronic properties of unsaturated nanoporous graphene

ABSTRACT The interaction sensitivity of unsaturated nanoporous graphene toward a series of gas molecules (O2, NO, NO2 and CO) was investigated by the first-principle calculation based on density functional theory. The most stable geometry configuration, adsorption energy, charge transfer, and electronic density of states of the complexes were thoroughly investigated, in which the gases were adsorbed on the unsaturated nanoporous graphene. It was found that all the gas molecules are strongly chemisorbed on the unsaturated nanoporous graphene. The enhanced adsorption energy and large charge transfer demonstrated a strong chemical adsorption interaction of gas molecules with the nanoporous graphene sheet. However, the electronic properties of the unsaturated nanoporous graphene are not very sensitive to all the gas molecules. It is suggested that the unsaturated nanoporous graphene might be suitable for sensing O2 and CO, while it could not be used for the NO and NO2.

Rational tuning towards A/B-sites double-occupying cobalt on tri-metallic spinel: Insights into its catalytic activity on toluene catalytic oxidation

Promoting the catalyst reducibility is the key to the breakthrough of the catalytic oxidation technology. We prepared the layered double oxides (LDOs) spinel catalysts utilizing the layered double hydroxides (LDHs) as precursors. Innovatively, cobalt was applied as A/B-sites double-occupying cations. By introducing Cu(II) into the A-sites, we created a pushing effect towards the A-sites Co(II). The binding energy of Co 2p and the projected density of states energy of Co 3d shifted higher. The Co(II) gained greater momentum to convert to Co(III). The same pushing effect towards B-sites Co(III) were generated using B-sites occupying Ga(III), promoting Co(III) transfer towards lower valence state. Thus, the converting between Co(II) and Co(III) were speeded up. Moreover, the ionic radius differences between Cu(II) and Co(II) caused lattice distortion, enhancing the adsorbed oxygen species and surface oxygen defects. These contributed to the great improvement of reducibility and enhanced catalytic activity towards toluene oxidation.

Adsorption behavior of Rh-doped MoS2 monolayer towards SO2, SOF2, SO2F2 based on DFT study

Abstract It is essential to detect the characteristic gas products of SF6 decomposition for fault diagnosis of gas-insulated switchgear (GIS). The model of Rh doped MoS2 was built by Materials Studio software. The micro process of three SF6 partial dissociation products (SO2, SOF2, SO2F2) approaching the Rh–MoS2 surface and reaching a stable state was simulated. The modification effect of Rh doped MoS2 was studied by the key adsorption parameters such as the adsorption structure, bandgap, absorption energy, charge transfer, the total and partial density of states and electron density difference. As a result, the electrical property and chemical activity are significantly improved in comparison with the pristine MoS2 monolayers by selecting the most stable Rh doping site. Simultaneously, it was found that Rh–MoS2 monolayer had good selectivity and gas sensitivity to SO2 and SOF2 with chemical adsorption. It can also be proved by the desorption time. From the adsorption energy, the adsorption reaction of SO2F2 is not strong, but the transferred charge is large.

Interaction studies of volatiles from jackfruit on α-phosphorene nanosheet—a DFT outlook

The present report brings out the interaction between the black phospherene nanosheet and volatile organic compounds (VOCs) originating from jackfruit using the first-principles calculation. Using the cohesive formation energy, the stable nature of the phospherene nanosheet is confirmed. The energy band structure provides the insights on the electronic properties of phospherene nanosheet and the energy gap is detected to be 0.59 eV, showing semiconductor nature. Besides, present results reveal the interaction of VOC compounds emitted from jackfruit (during various ripening stages). The adsorption of VOCs on phospherene nanosheet is in the following order isopentyl isovalerate > butyl isovalerate > isopentyl acetate > butyl acetate. The adsorption energy including energy gap, Bader charge transfer, and average energy gap variation clearly signifies the adsorption property of VOC compounds from jackfruit on phospherene nanosheet, which serves as the fingerprint to estimate the jackfruit freshness. Also, by using energy band structure, electron density, and density of states (DOS) maps, the adsorption property of VOC compounds have been explored. The result suggests that phospherene sheets can be used as a sensing material to estimate the quality of jackfruit.

Cosmological Constraints from Line Intensity Mapping with Interlopers

Abstract Understanding the formation and evolution of the universe is crucial for cosmological studies, and line intensity mapping provides a powerful tool for this kind of study. We propose to make use of multipole moments of a redshift-space line intensity power spectrum to constrain the cosmological and astrophysical parameters, such as the equation of state of dark energy, massive neutrinos, primordial non-Gaussianity, and star formation rate density. As an example, we generate mock data of multipole power spectra for Hα 6563 Å, [O iii] 5007 Å, and [O ii] 3727 Å measured by the SPHEREx experiment at z = 1 considering contaminations from interloper lines, and use the Markov Chain Monte Carlo method to constrain the parameters in the model. We find a good fitting result of the parameters compared to their fiducial values, which means that the multipole power spectrum can effectively distinguish signal and interloper lines, and break the degeneracies between parameters, such as line mean intensity and bias. We also explore the cross-power spectrum with the Chinese Space Station Telescope spectroscopic galaxy survey in the constraints. Since more accurate fitting results can be obtained by including measurements of the emission lines at higher redshifts out to at least z = 3, and cross-correlations between emission lines can be involved, line intensity mapping is expected to offer excellent results in future cosmological and astrophysical studies.

Observation of ultra-high energy density state with x-ray free electron laser SACLA

Typical inertial confinement fusion (ICF) plasmas have ultra-high energy density state (UHEDs) with an energy density exceeding 1 × 108 Jcm−3, which corresponds to a pressure of beyond 1 Gbar. In previous investigation, it is suggested that such an UHEDs condition could be generated with a tabletop ultrahigh intensity laser, by irradiating onto a nanowire array. In this research, we have developed to observe the laser energy absorption and transport mechanism in nanowire array samples with x-ray free electron laser facility SACLA. We obtained time-resolved snapshots of x-ray shadowgraph image with very high temporal resolution. From the measured images, however, the UHEDs might be generated only on very thin portion of the target surface because the mean density of the nanowire array was large. On the other hand, we observed significant rear surface expansion in late timing, suggesting that large laser energy deposition was achieved for the nanowire array samples.

Strangeness production with ALICE at the LHC

The main goal of the ALICE experiment is to study the physics of strongly interacting matter under extremely high temperature and energy density conditions to investigate the properties of the Quark-Gluon plasma (QGP). The enhanced production of strange hadrons with respect to non-strange particles was historically considered as one of the signatures of QGP formation during the evolution of the system created in heavy-ion collisions. The excellent tracking and particle identification capabilities of the ALICE experiment allow the reconstruction of multi-strange baryons via their weak decay channels over a large range of transverse momentum. The yields and the relative production rates of strange and multi-strange particles normalized to pions measured in pp, p–Pb, Pb–Pb and Xe–Xe collisions are presented as a function of particle multiplicity. The strangeness production dependence on the collision energy is also shown. Results are compared to QCD-inspired and statistical hadronization model predictions.

First-principles investigation of the structural stability and electronic properties of LiV1–xMxPO4F (M = Mn, Fe, Co, and Ni)

Density functional theory calculations corrected by on-site Coulomb interactions have been conducted to study the crystal structure and electronic property of the LiV1–xMxPO4F (M = Mn, Fe, Co, and Ni) electrode systems. The calculation results show that the substitution of V atoms in LiVPO4F by Fe-dopants resulted in the lowest formation energy, and the crystal structure is, therefore, most thermodynamically stable, while Co and Ni doping seems to be difficult due to their relatively higher formation energy than that of doping with Fe and Mn. Furthermore, Fe substitution can effectively suppress the volume change of the LiVPO4F materials during electrochemical delithiation, leading to improvement of the cycle performance of LiVPO4F electrode. The results of charge analysis predict that Fe substitution is able to donate extra electrons for charge compensation during the Li+ reversible extraction/insertion process. The calculation of energy band structure and density of states indicate that the Mn, Fe, Co, and Ni doping reduce the band gaps through variations of V-3d spin orbitals. However, only Fe doping introduced impurity level located at 0.75 eV above valence band in the forbidden band of LiVPO4F, providing a platform for electronic transition, which is helpful to enhance electronic conductivity of the LiVPO4F electrode.

A spherical crystal diffraction imager for Sandia's Z Pulsed Power Facility.

Sandia's Z Pulsed Power Facility is able to dynamically compress matter to extreme states with exceptional uniformity, duration, and size, which are ideal for investigating fundamental material properties of high energy density conditions. X-ray diffraction (XRD) is a key atomic scale probe since it provides direct observation of the compression and strain of the crystal lattice and is used to detect, identify, and quantify phase transitions. Because of the destructive nature of Z-Dynamic Material Property (DMP) experiments and low signal vs background emission levels of XRD, it is very challenging to detect a diffraction signal close to the Z-DMP load and to recover the data. We have developed a new Spherical Crystal Diffraction Imager (SCDI) diagnostic to relay and image the diffracted x-ray pattern away from the load debris field. The SCDI diagnostic utilizes the Z-Beamlet laser to generate 6.2-keV Mn-Heα x rays to probe a shock-compressed material on the Z-DMP load. A spherically bent crystal composed of highly oriented pyrolytic graphite is used to collect and focus the diffracted x rays into a 1-in. thick tungsten housing, where an image plate is used to record the data.