Equilibrium Distance Research Articles

Probing lattice vibration of alkali halide crystals by broadband terahertz spectroscopy

Terahertz spectral features of alkali halide crystals were studied with the combination of broadband terahertz time-domain spectroscopy and the solid-state-based density functional theory calculations. To understand the particular modes of the observed terahertz features of the alkali halide crystals, the resonant modes of KCl and CsCl were analyzed using face-centered cubic and body-centered cubic lattice models, respectively. The results show that the characteristic terahertz absorption peaks could be assigned to the lattice vibration of the ionic crystals. Furthermore, the terahertz responses of a series of alkali halides were recorded, and obvious absorption peaks were observed in each salt in the frequency region below 8.5 THz. What is more interestingly is that the frequencies of these observed peaks are red-shifted with the increases of the mass and radius of the ions. This correlation between the resonant frequency of the lattice vibration, the reduced atomic mass, and the equilibrium distance between the ions agrees well with the harmonic oscillator model.

Interactive multilevel programming approaches in neutrosophic environments

Multilevel programming is a mathematical programming problem with hierarchical structure. A typical feature of multilevel programming is that the upper level exhibits a priority over the lower level. However, the solutions obtained by most existing programming methods either violate this rule or ignore the participants’ desire for a win–win outcome. The objective of this study is to propose new multilevel programming approaches for obtaining desirable solutions. First, three types of membership functions in neutrosophic set are defined to comprehensively describe fuzzy cognition of decision makers. Then, considering dissimilar intentions of experts, three different interactive approaches are proposed to solve multilevel programming problems. To demonstrate the feasibility of the proposed approaches, a case of pricing decision-making of data products is investigated and the impacts of four key parameters are discussed. Finally, several numerical examples are studied by using the proposed approaches and other existing methods. Two evaluation indexes, the equilibrium coefficient and distance measure, are utilized to appraise the performance of the developed programming methods. The results demonstrate that the proposed approaches can obtain sound solutions which obey the rule of multilevel programming, realize the mutual benefits of participants, and can provide guidelines for the pricing of satellite image data products.

DFT and experimental study of elemental mercury (Hg0) removal by 2D-g-C3N4

2D-g-C3N4 nanosheet was prepared and employed for the adsorption of elemental mercury (Hg0). The g-C3N4 was analyzed through X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) methods, and the results showed that the prepared sample was well-defined 2D-nanosheet. The 2D-g-C3N4 sorbent exhibited a high Hg0 removal efficiency (> 90%) at the condition of temperature 120 °C. To investigate the mechanism of Hg0 adsorption on the 2D-g-C3N4 surface, corresponding theoretical exploration based on the first principle prediction and X-ray photoelectron spectroscopy (XPS) test was implemented. The DFT calculation results showed that Hg0 was strongly bound to the B1 site of the g-C3N4 surface with an adsorption energy change of -162.2 kJ mol−1, the equilibrium distance of Hg-C was 3.473 Å, and electron transfer between Hg and C atoms was 0.02. The results of XPS showed the main species of mercury was HgO on the surface of 2D-g-C3N4 sample and the interaction between C3N4 surface and Hg0 was physisorption. This study provides a demonstration of proof-of-concept demonstration that g-C3N4 is a promising sorbent capable of capturing Hg0, and presents in-depth understanding of Hg0 adsorption mechanism on 2D-g-C3N4 sorbent.

Flow-mediated organization of two freely flapping swimmers

Abstract

Microwave-hydrothermal synthesis of copper sulphide nanorods embedded on graphene sheets as an efficient electrocatalyst for excellent hydrogen evolution reaction

Fabrication of non-precious and highly efficient electro-catalyst to accelerate the production of hydrogen evolution reaction (HER) at lower potential is a great challenging task in today’s energy generation era. In the present work, copper sulphide (CuS) nanorods tailored on reduced graphene oxide (rGO) nanosheets were synthesised by microwave-assisted hydrothermal method for highly stable and efficient material for HER is reported to newest. CuS nanorods decorated on rGO sheets showed a very low onset potential value of 0.0891 V with high current density when compared to pure CuS, rGO and better than commercially available Pt/C in 0.5 M H2SO4 solution with 100% Faradaic yield in HER activity. Importantly the present synthesis approach can be readily extended to prepare composites of CuS tailored structure and morphology for potential application in energy storage and conversion. The CuS@rGO nanocomposites can strongly accommodate a large volume changes by supplying the conducting network and in turn increasing the charge transferability. Oxygen cluster ions and sulphur edges on Cu surface that decreases the interface equilibrium distance between CuS, rGO and strong interactive coordination showing excellent synergism.

Hydrogen-molecule spectrum by the many-body GW approximation and the Bethe-Salpeter equation

We check the ab initio GW approximation and Bethe-Salpeter equation (BSE) many-body methodology against the exact solution benchmark of the hydrogen molecule H$_2$ ground state and excitation spectrum, and in comparison with the configuration interaction (CI) and time-dependent Hartree-Fock methods. The comparison is made on all the states we could unambiguously identify from the excitonic wave functions' symmetry. At the equilibrium distance $R = 1.4 \, a_0$, the GW+BSE energy levels are in good agreement with the exact results, with an accuracy of 0.1~0.2 eV. GW+BSE potential-energy curves are also in good agreement with the CI and the exact result up to $2.3 \, a_0$. The solution no longer exists beyond $3.0 \, a_0$ for triplets ($4.3 \, a_0$ for singlets) due to instability of the ground state. We tried to improve the GW reference ground state by a renormalized random-phase approximation (r-RPA), but this did not solve the problem.

Experiment and theory for acetylene adsorption in transformer oil

A series of nanofluids were prepared by incorporating titanium dioxide (TiO2), carbon nanotube (CNTs) and zinc oxide (ZnO) into transformer oils to eliminate acetylene (C2H2) bubbles, and elimination of the partial discharge (PD). The adsorption of C2H2 molecules onto three model nanoparticles (TiO2, CNTs and ZnO) were simulated based on density functional theory (DFT) calculations, and then compared with experimental data. Theoretically, TiO2 showed the highest capacity for adsorbing C2H2 molecules among the studied nanoparticles, as featured by a high adsorption energy (3.61 eV), high charge transfer (1.34 eV), and low equilibrium distance between TiO2 and C2H2 (2.55 Å). The maximum breakdown voltage was obtained at optimum CNTs, ZnO and TiO2 contents of 0.01, 0.01, and 0.075 wt.%, respectively. Experimental results confirmed theoretical calculations; so that TiO2 had the highest efficiency of C2H2 adsorption (71%), while ZnO and CNTs could adsorb acetylene by 64% and 17%, respectively. Moreover, CNTs and ZnO unenviably decreased the breakdown voltage by 77% and 27%, respectively, while TiO2 increased it by 13%. Therefore, TiO2-based nanofluids not merely decreased the adverse effects of PD, but also improved the electrical properties of the transformer oil.

Equilibrium distances for the capillary interaction between floating objects.

When small objects are placed at a water-air interface, attractive and repulsive interactions appear due to liquid deformations. Although it is commonly admitted that two floating objects deforming the liquid interface in the same way are only attracting, we show that in the case of objects whose height does not vary during the interaction, the situation is much more complex than expected. In fact, attraction and repulsion can coexist at different ranges, so that equilibrium distances are observed. A 1D model based on the capillary interaction between vertical plates immersed in water is used to illustrate and calculate these situations, giving a picture of capillary interactions. We show that the wetting condition plays a determinant role in the behaviour of the interaction between floating objects. We also demonstrate that the equilibrium distance is given by the logarithm of the capillary charge ratio, using the right capillary charge definition. We also discuss the particular case of the existence of an interaction with a zero-capillary charge. A general equation of the equilibrium distance is proposed. An experimental confirmation of this relation is also given.

On the relationship between spectroscopic constants of diatomic molecules: a machine learning approach.

Through a machine learning approach, we show that the equilibrium distance, harmonic vibrational frequency and binding energy of diatomic molecules are related, independently of the nature of the bond of a molecule; they depend solely on the group and period of the constituent atoms. As a result, we show that by employing the group and period of the atoms that form a molecule, the spectroscopic constants are predicted with an accuracy of <5%, whereas for the A-excited electronic state it is needed to include other atomic properties leading to an accuracy of <11%.

Molecular dynamics simulation of contact behaviors between multiwall carbon nanotube and metal surface

The interfacial contact configuration and contact intensity between carbon nanotube and metal surface play an important role in the electrical performance of carbon nanotube field effect transistors and nanoscale carbon nanotube robotic manipulation. In this paper, we investigate numerically the contact configuration and the contact intensity between multiwall carbon nanotube with open ends or capped ends and various metal surfaces in carbon nanotube field effect transistor assembly by the molecular dynamics simulation. The simulation results show that the change in the position and shape of multiwall carbon nanotube on the metal surface are mainly due to the decrease of van der Waals energy reduction: the decrement of van der Waals energy is converted into the internal energy and kinetic energy of carbon nanotubes. Moreover, the binding energy between multiwall carbon nanotube and metal surface is negative, which indicates that multiwall carbon nanotube adheres to the metal surface. In addition, the contact intensity of multiwall carbon nanotube in horizontally contacting metal surface is influenced by initial distance, contact length and metal materials. The final equilibrium distance is around ~0.3 nm when the initial distance is less than ~1 nm. And the contact intensity increases with the augment of contact length between carbon nanotube and metal. The contact intensity between platinum and carbon nanotube is larger than that between tungsten and aluminum, therefore, platinum-coated probe is generally utilized for picking carbon nanotube up. The contact intensity of the carbon nanotubes with the open ends and closed ends in the vertical contact with the metal surface are both lower than those in the horizontal contact. The interfacial contact configuration of carbon nanotube and metal materials mainly include the displacement and geometric deformation of carbon nanotube. The displacement and geometric deformation of multiwall carbon nanotube with open ends on the metal surface finally result in its radial nanoscale ribbon structure. But the closed-end three-wall carbon nanotube has the small axial geometric deformation through comparing the concentration profiles between the initial carbon nanotube and the collapsed carbon nanotube. In a carbon nanotube field effect transistor, the collapsed multiwall carbon nanotube forms the ribbon structure like a single wall carbon nanotube. And the distance between carbon nanotube walls and between the outermost carbon nanotube wall and the metal electrode are both about ~0.34 nm. The atomic scale spacing ensures that electrons tunnel from the metal to the outermost carbon nanotube wall and migrate radially between the inner carbon nanotube walls.

Relativistic treatment of alkaline earth dimers in the presence of non-central molecular potential in N-dimensions

Abstract Within the framework of relativistic theory, N-dimensional non-central Morse potential as anharmonic model is considered thoroughly to describe the internuclear motion of alkaline earth dimers in the different electronic states. We illustrate the surface plots of alkaline earth dimers to examine the effect of angular potential, due to existence of molecular systems in which spherical symmetry disappears. Also, the contribution of angle dependent interaction to the relativistic energy spectra has been investigated in N-dimensions. We determine the relativistic vibrational transition frequencies in the lower vibrational states for the X 1 Σ g + ground state of 24 Mg 2 , 40 Ca 2 , 24 Mg 40 Ca and A 1 Σ u + excited state of 88 Sr 2 alkaline earth diatomic molecules. The theoretical results have been compared with Rydberg-Klein-Rees (RKR) and the inverted perturbation approach (IPA) experimental data. We also discussed the validity of Pekeris approximation around the equilibrium distance as well as the repulsive and attractive regions for alkaline earth dimers.

Potential Energy Surfaces without Unphysical Discontinuities: The Coulomb Hole Plus Screened Exchange Approach.

In this work, we show the advantages of using the Coulomb hole plus screened exchange (COHSEX) approach in the calculation of potential energy surfaces (PES). In particular, we demonstrate that, unlike perturbative GW and partial self-consistent GW approaches, such as eigenvalue self-consistent GW and quasi-particle (QP) self-consistent GW, the COHSEX approach yields smooth PES without irregularities and discontinuities. Moreover, we show that the ground-state PES obtained from the Bethe-Salpeter equation (BSE), within the adiabatic connection fluctuation dissipation theorem, built with QP energies obtained from perturbative COHSEX on top of Hartree-Fock (BSE@COHSEX@HF) yield very accurate results for diatomic molecules close to their equilibrium distance. When self-consistent COHSEX QP energies and orbitals are used to build the BSE equation, the results become independent of the starting point. We show that self-consistency worsens the total energies but improves the equilibrium distances with respect to BSE@COHSEX@HF. This is mainly due to the changes in the screening inside the BSE.

Detection of nucleobases on borophene nanosheet: A DFT investigation

In this paper, we present a computational study investigating the electronic properties of DNA nucleobases (Adenine, Guanine, Cytosine and Thymine) on χ3 borophene using a combination of density functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism.The adsorption energy, equilibrium distance, net charge of transfer, and density of states (DOSs) are obtained at different molecule orientations and selective positions.The most stable geometries of DNA molecules on χ3 borophene are also determined.By using (NEGF) formalism, the electronic transmission and electrical current are calculated separately as a function of applied bias voltage for each nucleobase. We find that attaching this molecule to borophene changes the electrical conductivity.Results indicate the strong potential of borophene in adsorption of the DNA molecules, meaning this two-dimensional material could be a suitable candidate for future DNA sequencing devices.

High Temperature Sealing of Silicon Oxide/Oxide Bonding Interfaces

High temperature (>1000°C) annealing is necessary to completely close a bonding interface. Using interface synchrotron high energy X-ray reflectivity, we have investigated the sealing behavior of silicon thermal oxide/ silicon thermal oxide interfaces, with different surface roughnesses. Interface X-ray reflection is able to measure accurately the width and the depth of the electron density gap across a bonding interface with a sub-nanometer accuracy, whose product is a good marker of the interface closure.The uncomplete closure of the interface is the result of a balance between attractive and repulsive force between the two bonded solids. These two forces depend on the statistics of asperity and on the mechanical behavior of individual asperity [1]. For attraction, at high temperatures, a key factor is the gain of contact surface area which reduces the surface energy due to uncontacted zones. Repulsion is due to compression of contacting asperities. At high temperature, both elastic and plastic behavior can be expected, with some yield of the asperities compressed above the elastic limit.In the elastic solid regime, we have shown that equilibrium distance of rough silicon oxide to rough siliconoxide bonding can be predicted using standard adhesive contact models such as Johnson-Kendall Roberts (JKR) or Deryagin-Müller-Toporov (DMT) with Gaussian roughness statistics[2]. The equilibrium distance is dependent and sensitive to the Fuller Tabor adhesion parameter, θ=E σ3/2 R1/2 / 2γR where E is the Young modulus, σ the mean roughness, R the radius of the asperity, while 2γ is the adhesion energy at contact points. When θ>>1 , the equilibrium distance is large and the contact area is small (unclosed interface) . When θ<<1 the adhesion energy is strong and the system will have a strong tendency to seal.In the plastic regime, both repulsive and attractive curves share the same dependence with distance so that the system is expected to be unstable, between a weakly evolving unsealed interface and a fully sealed interface when the asperity pressure stress is above the elastic limit.The kinetics of the sealing can also be modeled in this case, monitoring the interfacial gap as a function of time (Figure). It is found that the sealing characteristic time scales directly with the silicon oxide viscosity (Figure insert). This dependence can be understood using the plastic asperity contact model, assuming the fluid part flows according to the Stokes equation around asperities.

Effects of perturbation order and basis set on alchemical predictions.

Alchemical perturbation density functional theory has been shown to be an efficient and computationally inexpensive way to explore chemical compound space. We investigate approximations made, in terms of atomic basis sets and the perturbation order, introduce an electron-density based estimate of errors of the alchemical prediction, and propose a correction for effects due to basis set incompleteness. Our numerical analysis of potential energy estimates, and resulting binding curves, is based on coupled-cluster single double (CCSD) reference results and is limited to all neutral diatomics with 14 electrons (AlH⋯NN). The method predicts binding energy, equilibrium distance, and vibrational frequencies of neighboring out-of-sample diatomics with near CCSD quality using perturbations up to the fifth order. We also discuss simultaneous alchemical mutations at multiple sites in benzene.

Spectroscopy, lifetime, and charge-displacement of the methanol-noble gas complexes: An integrated experimental-theoretical investigation

An integrated experimental-theoretical investigation was employed to determine rovibrational energies, spectroscopic constants, lifetime as a function of temperature in gas phase complexes of methanol with noble gas (NgHe, Ne, Ar, Kr, Xe, and Rn). Beside that, a parallel effort has been addressed to theoretically characterize the nature of intermolecular interactions determining the dissociation energy and equilibrium distance of the formed adducts. Dynamics and lifetime results reveal that, except for the CH3OH-He aggregate, all other methanol-Ng compounds are sufficiently stable under thermal conditions. Their lifetimes are larger than 1ps for the temperature of the bulk in the range between 200 and 500K. In addition, the current lifetime results suggest that the aggregates formed by methanol and Ng are globally more stable than corresponding complexes formed by water with Ng. From the point of view of the CCSD(T)/aug-cc-pVTZ level calculation, in all compounds, the electron densities of Ng partners are weakly polarized in the presence of CH3OH molecule. The charge-displacement curves and NBO analysis indicate that the charge transfer from Ng to methanol molecule, in general, plays a minor role, being appreciable only in the aggregate involving Ar. Finally, it was verified from the SAPT2+(CCD)-δMP2/aug-cc-pVTZ calculations and NCI analysis that the dispersion is the essential long-range attractive contribution to the interaction energy for all studied complexes. This feature strongly suggests that these compounds are held bonded substantially by van der Waals forces. Then non-covalent intermolecular bonds are effectively formed in the gas phase, which is disturbed by small stabilizing charge-transfer contributions.

The spatially oriented redistribute of photogenerated carriers and photocatalytic hydrogen evolution mechanism research on polymeric carbon nitride Van der Waals homojunction

The weaker interlayer Van der Waals force of polymeric carbon nitride (PCN) increases the potential barrier of electron transfer between layers, which greatly inhibits the carrier separation efficiency of PCN. Herein, we designed and prepared Van der Waals homojunction of PCN (VHPCN), which the interlayer Van der Waals force forces were instead by Coulomb force. DFT calculated reveals that the equilibrium distance and the interface adhesion energy of VHPCN were significantly decreased and enhanced, respectively, under the function of Coulomb force. The equilibrium distance decreased from 3.27 Å to 2.49 Å and the interface adhesion energy enhanced from −0.35 eV to −1.78 eV. This structure not only the transfer distance of electrons at the interface is effectively decreased, but also the transfer barrier of electrons at the interface is reduced. Thus, the electrons/holes pairs in the VHPCN photocatalyst present the phenomenon of oriented interlayer transfer and ultrahigh carrier separation efficiency under the synergistic effect between the built-in electric field and the interlayer Coulomb force of the Van der Waals homojunction. The optimal VHPCN exhibited the photocatalytic H2 evolution rate and apparent quantum yield (AQY), which are 7.9 mmol·g−1·h−1 and 32.4% (>420 nm), respectively. This work put forward a promising strategy to construct novel Van der Waals homojunction within 2D materials for the desirable photogeneration carrier spatially distribution controlling, which could be generalized to other 2D materials for photocatalytic applications in the advanced energy and environmental field.

First-principles investigation of grain boundary structure effects on hydrogen solubility and segregation in tungsten

ABSTRACT Hydrogen (H) solubility, segregation, and hydrogen-induced intergranular fractures in eight symmetric tilt grain boundaries (GBs) in tungsten (W) are investigated through the first-principles calculations. The results show that there is an equilibrium distance, about 1.95 Å, between the H inserted in interstitial sites and its nearest W. Interactions between the inserted H and GBs are rather localized, thus the local environments of interstitial sites are responsible for the hydrogen solubility. The hydrogen solution energy decreases as the hard-sphere radius of the interstitial site increases. But the trend slows significantly down as the is larger than 0.57 Å, which is corresponding to the equilibrium H-W distance of 1.95 Å, due to the ignorable contributions from lattice distortions induced by the inserted H to the hydrogen solution energy. It is found out that the GBs with smaller interstitial site are more resistant to hydrogen segregation as well as the hydrogen-induced intergranular fractures. Among all GBs studied here, the twin GB ∑3(110)[111] has the smallest interstitial site; hence, it has the weakest capability to trap H and it is also the most resistant to hydrogen-induced intergranular fractures. Our results provide a sound guide to design GBs to suppress hydrogen-induced intergranular fractures.

Effect of adsorption sensitivity of armchair single-walled BN nanotube toward thiocyanate anion: A systematic evaluation of length and diameter effects

The first-principles calculations to investigate the adsorption behavior of thiocyanate anion (SCN−) on the external surface of H-capped (6, 0), (3, 3), and Al and Ga doped (3, 3) single-walled boron nitride nanotubes (SWBNNTs) has been performed. Binding energy and the equilibrium distance corresponding to the most stable state of SCN−/(3, 3) BNNT is found to be −1.747 eV and 1.546 A, respectively, which can represent mainly a polar covalent bond. The calculation results have shown that both doped aluminum and gallium can enhance the adsorption energy of SCN− into the (3, 3) BNNTs. For the SCN− /BNNT complexes, the energy gaps, NBO, dipole moments, natural atomic orbital occupancies and global indices have been computed using DFT theoretical method at B3LYP level and 6–31G** basis set. Finally, a novel type of the adsorbent that can be used to remove of SCN− anion has been reported.

Transportation can cancel out the ecological advantages of producing organic cacao: The carbon footprint of the globalized agrifood system of ecuadorian chocolate

Under the hypothesis that organically managed cacao agroforestry systems report a lower global warming potential (GWP) and reduce other environmental pressure indicators compared with conventionally managed systems and monocultures, this work discusses how global transportation can cut back the ecological advantage of the production phase. For this purpose, the life cycle assessment (LCA) of 1 kg of dark chocolate manufactured with Ecuadorian cacao has been performed (cradle-to-retailer approach), including the indirect impacts of transportation and estimating the equilibrium distances beyond which organic chocolate would have a higher impact than chocolate manufactured from cacao grown in monocultures and/or conventionally managed systems. To articulate the discussion, the carbon footprint (CF) of cacao/chocolate was analyzed together with 10 additional LCA-related impact categories. Three management systems—conventional monoculture (CM) and agroforestry (CA), and organic agroforestry (OA)—and three different supply chain scenarios with different weights in the transportation phase were studied. Expanding on the concept of “food miles”, the equivalent kilometers of the impact of emissions (km-eq) (or cumulated energy demand, eutrophication, etc.) were defined as the variable distance that a certain means of transportation can travel in relation to a fixed level of GHG emissions (or MJ, kg PO4-eq, etc.). The CF of the life cycle of cacao/chocolate was estimated at between 2.04 and 4.66 kg CO2-eq kg−1. The relative weight of transportation in relation to the total GHG emissions ranged between 8.9% and 51.1%, with cacao/chocolate traveling between 1380 and 9155 km-eq. The CF of chocolate made from cacao grown in OA systems was 22.7%–34.2% and 6.3%–10.7% lower than the CF of chocolate produced from cacao grown in CM and CA and manufactured and transported under the same conditions. The equilibrium distances between managements were estimated at 1213 and 5275 km-eq. Beyond those equivalent kilometers, organic chocolate would have a larger CF than chocolate manufactured from cacao grown, respectively, in CA and CM systems. Our results indicate that transportation would cancel out this and most other comparative ecological advantages of producing organic cacao analyzed in this work. Directly exporting chocolate from cacao-producing countries and relocating chocolate manufacture would help reduce GHG emissions and other environmental impacts of the supply chain.