Density Of States Analysis Research Articles

Adsorption Properties and Quantum Molecular Descriptors of the Anticancer Drug Cytophosphane on the Armchair Single-Walled Carbon Nanotubes: A DFT Study

Abstract: In the current work, the adsorption of cytophosphane (cytophosphane is a chemotherapeutic drug and is used to treat several specific autoimmune diseases and malignant processes) on the (5,5) SWCNT was studied using density functional theory (DFT) calculations in terms of geometry, energy gap, charge transfer, molecular electrostatic potential surface, and density of state analysis. The behavior of the binding properties and the electronic structures revealed that the cytophosphane molecule could be adsorbed on the SWCNT by the adsorption energy of approximately -100.3 kcal mol-1. Also, it was found that the electronic properties of the SWCNT are very sensitive to the presence of cytophosphane molecules so that the energy gap of the nanotube is changed about 61% after the adsorption process. Based on calculated results, the SWCNT is expected to be suitable as a drug carrier for the delivery of cytophosphane drug.

Carbazole-based donor materials with enhanced photovoltaic parameters for organic solar cells and hole-transport materials for efficient perovskite solar cells.

Five carbazole-based donor molecules are designed by structural engineering of reference molecule PF. The molecules are devised by substitution of thiophene bridged end-capped acceptor groups namely (2-methylenemalononitrile) PF1, (methyl 2-cyanoacrylate) PF2, (3-methyl-5-methylene-2-thioxothiazolidin-4-one) PF3, (2-(3-methyl-5-methylene-4-oxothiazolidin-2- ylidene) malononitrile) PF4, and (4-(5-methylthiophen-2-yl) benzo[c] [1, 2, 5] thiadiazol) PF5. A DFT investigation was performed at the selected DFT functional MPW1PW91/6-31G (d,p) to investigate the optoelectronic properties of PF and all designed (PF1-PF2) molecules. Several important characteristics, i.e., band gap (Eg), transition density matrix analysis, dipole moment (µ), density of states analysis, reorganization energies, open circuit voltage (Voc), and fill factor, were investigated. The comparison of energy levels of reference molecule and designed molecules unveils the fact that these molecules are efficient hole transport materials to be used in perovskite solar cells (PSCs). All the newly drafted molecules (PF1-PF5) show higher λmax values in solvent (Chlorobenzene) ranging from 529 to 614nm than the reference PF (344nm). Smaller band gap (Eg) values in a range of 2.27-1.9eV for newly designed molecules are observed which are very much reduced when compared to reference PF. Lowered exciton binding energies (Eb) and reorganization energies for the electron (0.004279-0.0103337eV) as compared to PF reveal that our molecules display higher electron mobility rates, and hence, these small molecules can be used as proficient donor materials in high-performance organic solar cells (OSCs) and better hole transport materials (HTMs) for possible application in perovskite solar cells.

Structural evolution and bonding characteristics of neutral Cs2B n clusters

In this study, the unbiased crystal structure analysis by particle swarm optimisation (CALYPSO) combined with the density functional theory (DFT) method were used to perform a structure search for neutral Cs2B n (n = 1–12) clusters, as well as the corresponding global minimum of the potential energy surface were determined. The ground-state structures of the Cs2B n (n = 1–12) clusters have four types of geometries: planar, arch bridge, double pyramid, and shield shape. Subsequently, the relative stability of the ground-state structures was systematically analysed based on three effective rules, which indicates that the C7V Cs2B8 with a double pyramid structure has unusual stability. The results of the molecular orbitals (MOs) and density of states analysis (DOS) show that the B-2s and 2p atomic orbitals of Cs2B8 are the main components of MOs. In addition, from the results of adaptive natural density partitioning (AdNDP) and localised orbital locator (LOL), it can be seen that the excellent stability of Cs2B8 originates from the delocalised large π bonds with aromaticity and the s–p bonding of B–B. Our results reveal the structural growth mode of Cs2B n clusters and enrich the chemical bonding properties of boron-based clusters.

Trapping Hydrogen Atoms in Vacancies of Li2TiO3 Crystal: A First-Principles Study.

The hydrogen atom capacity in the vacancies of the Li2TiO3 crystal is systematically studied by the first-principles method to evaluate its tritium release performance as a solid breeder material in nuclear fusion reactors. The adsorption process of adding hydrogen atoms one by one in the vacancy are investigated to find the possible adsorption sites of the hydrogen atoms in the vacancy. The charge transfer and density of states analysis are performed to reveal the form of a hydrogen–hydrogen dimer in the vacancy. Also, the trapping energy and formation energy are defined and calculated to determine the hydrogen atom capacity of the system. According to the simulations, the Ti vacancies have the strongest hydrogen atom capacity followed by Li vacancies, and O vacancies are the weakest. The influence of hydrostatic pressure on the hydrogen atom capacity is also investigated. Our results reveal the hydrogen capacity of vacancies in the Li2TiO3 crystal from the atomic scale, which also provide a theoretical guide to the related tritium release experiments.

First‐principles calculation of mechanical properties and electronic structures of W 4 Co 4− n X n B 4 (X = V, Mn, Fe, Ni; n = 0,1)

The first-principles calculation is performed to explore the mechanical properties and electronic structures of transition elements X (X = V, Mn, Fe, Ni) doped WCoB (tungsten cobalt boron), which has shown high oxidation resistance and melting point under high pressure. The energy analysis indicates that the high pressure leads to the lower lattice constants and less stable structures. The deviation of cohesive energy and formation enthalpy between doped and undoped structures indicates that W4Co3FeB4 and W4Co3NiB4 have similar stability. The high pressure contributes to the increasing of elastic, shear, and bulk moduli, which indicates the increase of covalence. The increase of Poisson's ratio, B/G ratio, and anisotropy index AU indicates the higher ductility and higher anisotropy under high pressure. Based on bulk modulus and shear modulus, the hardness of W4Co4B4, W4Co3FeB4, and W4Co3NiB4 increases under high pressure, which consists of the variation of electronic structures. The density of states (DOS) and partial DOS analysis indicate that the high pressure leads to lower density around Fermi level and higher hybridization. W4Co4B4, W4Co3FeB4, and W4Co3NiB4 show similar variation of mechanical properties, which is determined by the similar atom properties of Co, Fe, and Ni. Similarly, W4Co3VB4 and W4Co3MnB4 also imply similar variation of mechanical properties and electronic structures.

Atomic-Scale Insights into Comparative Mechanisms and Kinetics of Na–S and Li–S Batteries

The Na–S and Li–S batteries are in the forefront to supplant ubiquitously used lithium-ion batteries. The understanding of mechanistic differences between Na–S and Li–S is critical to enable the inter-transfer of developed technologies toward designing high-performance cathode materials. The anchoring materials (AMs) are required to overcome the performance-limiting factors such as sluggish kinetics of metal polysulfides’ (M2Sn, M = Na and Li, n = 1–8) conversion reactions and their dissolution into electrolytes. This study undertakes the challenges to critically understand the role of AMs on the polysulfide chemistry in both the batteries. We employ first-principles density functional theory simulations to comprehensively examine the adsorption mechanisms of M2Sn and the kinetics of sulfur reduction reactions (SRRs) and the catalytic decomposition of short-chain polysulfides across Na–S and Li–S batteries on pristine and vanadium (V) single-atom catalyst embedded WSe2 (V@WSe2) substrates. We found that pristine WSe2 cannot immobilize the higher-order M2Sn; however, V@WSe2 endows adequate binding energies to trap the higher-order M2Sn. The degree of M2Sn adsorption strengths and the effectiveness of the V@WSe2 varies between Na–S and Li–S systems. We elucidate the underlying mechanistic details with the aid of charge transfer, bond strength, and density of state analysis. Importantly, our simulations reveal that, in V@WSe2, the rate-limiting step of the SRR is kinetically faster in Li–S, whereas the oxidative decomposition of the discharge end product M2S exhibits accelerated kinetics in Na–S batteries. These findings are pivotal to understand the role of AMs in the design of cathode materials for addressing the performance-limiting factors in Na–S and Li–S batteries, in particular, and metal–sulfur batteries, in general.

Prediction and molecular mechanism of phosphate adsorption by metal oxides

<p indent="0mm">Metal oxide adsorbents have emerged as promising phosphate removal materials due to their excellent adsorption performance, low price, and stability. However, the relationship between the structure of metal oxides and the performance of phosphate adsorption is still unclear, and the molecular mechanism of phosphate adsorption by metal oxides remains to be elucidated. Understanding the major influencing factors and mechanisms of phosphate adsorption by metal oxides is critical for the design of metal-based materials for phosphate adsorption. In this study, the kinetics and thermodynamics of phosphate adsorption by Gd₂O₃ and CeO₂ were analyzed, and the phosphate adsorption capacity of 32 metal oxides was determined. ReliefF algorithm was used to identify the key descriptors of metal oxides affecting phosphate adsorption. Based on the descriptors, prediction models for phosphate adsorption were developed based on six machine learning algorithms, and the applicability domain of the models was characterized. Phosphate adsorption on the surface of six typical metal oxides was investigated by using molecular simulations based on density functional theory (DFT). The results demonstrated that the maximum adsorption capacity of Gd₂O₃ for phosphate was 4.14 times higher than that of CeO₂. The crystal structure of Gd₂O₃ was changed after adsorbing phosphate and resulted in Gd₂O₃ transformation into urchin shaped structures, but the crystal structure of CeO₂ remained basically unchanged before and after adsorption. The results of phosphate adsorption of 32 metal oxides showed that rare earth metal oxides (except CeO₂) and ZnO had higher adsorption capacity than other metal oxides. The electronegativity and cationic charge of metal oxides were identified as two important factors for phosphate adsorption using ReliefF algorithm. Six machine learning algorithms were utilized to build the prediction models for screening metal oxides with high adsorption capacity, and the predictive accuracy of the decision tree model exceeded 90% for both training and test sets. Classification rules of the decision tree model indicated that metal oxides with electronegativity ≤ 1.23 had high adsorption potential for phosphate. Characterization of the model’s applicability domain showed that all metal oxides were within the applicability domain. DFT analysis showed that adsorption energies of Gd₂O₃ and Y₂O₃ for phosphate were −3.97 and <sc>−4.56 eV,</sc> which were higher than those of CeO₂, NiO, ZnO and Cr₂O₃<sc>(–1.61− –0.26 eV).</sc> The adsorption configuration of Gd₂O₃ and Y₂O₃ with higher adsorption energy for phosphate was bidentate binuclear, while that of CeO₂, NiO, ZnO and Cr₂O₃ with lower adsorption energy was monodentate mononuclear. Combined with molecular orbital theory and density of states analysis, it was found that the d orbitals from Gd and Y atoms higher than the Fermi level interact with the p orbitals of the oxygen atom from the phosphate, splitting into antibonding orbitals higher than the Fermi level. Theoretical calculations revealed a new mechanism that the d orbitals energy level of metal atoms determines the phosphate adsorption energy. The prediction model established in this study can provide a basis for screening metal-based materials that can effectively adsorb phosphate, and the molecular mechanism deciphered by DFT calculations can provide a theoretical basis for the design of adsorbents.

First principles calculations investigation of optoelectronic properties and photocatalytic CO2 reduction of (MoSi2N4)5-n/(MoSiGeN4)n in-plane heterostructures

In-plane (MoSi2N4)5-n/(MoSiGeN4)n heterostructures have been delicately designed and systematically studied using first-principles density functional theory calculations. Such heterostructures exhibit dynamical stability as verified by calculated phonon dispersion spectra. The calculated band gap values increase with the MoSi2N4 area increase, as 1.385(1.860) eV for (MoSi2N4)0/(MoSiGeN4)5 and 1.925(2.385) eV for (MoSi2N4)5/(MoSiGeN4)0 using PBE (HSE06). By density of states analysis, the Ge 4p state made an excellent contribution to moving up the conduction band position and altering the band gap value. Also, the work function values can be modulated by the n numbers of (MoSi2N4)5-n/(MoSiGeN4)n. Based on optical and redox potential calculations, the calculated results suggest that the (MoSi2N4)5-n/(MoSiGeN4)n heterostructures have the potentials to be applied as ideal photocatalysts for photocatalytic CO2 reduction. Notably, different photocatalytic reduction reaction products can be formed using such (MoSi2N4)5-n/(MoSiGeN4)n in-plane heterostructures with different n values, indicating that selective catalytic reduction reactions can be realized on the in-plane heterostructures. Our findings suggest that (MoSi2N4)5-n/(MoSiGeN4)n monolayer in-plane heterostructures can serve as a new class of 2D materials for photovoltaic and photocatalysis applications, providing insightful guidance for the development of optoelectronic devices.

New Cu(II) and Zn(II) complexes with diethyl phenyl (N-phenylsulfamoylamino) methyl phosphonate: Synthesis, characterisation, DFT/M11 studies, NBO, DOS, QTAIM and RDG analysis

The stability constants (βij) and the thermodynamic parameters (ΔH°, ΔS° and ΔG°) of the complexes between diethyl phenyl (N-phenylsulfamoylamino) methyl phosphonate with Cu(II) and/or Zn(II) ions were determined by UV-visible spectrophotometric measurements in methanol at room temperature. The stable (1:2) solid-state mononuclear complexes were synthesised and characterised by FTIR, 1H-NMR, elemental analysis and magnetic moment measurements. In the DFT study, the predicted structural parameters with four exchange-correlation functionals were compared with experimental data. Their performance in predicting the vibration frequencies was also tested. Subsequently, with the best functionals thus obtained, calculations were performed on the most stable (1:2) complexes to obtain information on their structures and properties. The most stable geometrical structure, structural parameters, vibrational frequencies, UV-vis absorption spectra and global reactivity indices were carried out. The calculated results were in good agreement with the experimental findings. In order to gain further insights on the complexes properties non-linear optics (NLO), natural bond orbital (NBO), density of states (DOS) and quantum theory of atoms in molecule (QTAIM) analyses were performed. In addition, attractive bonds and van der Waals interactions were explored and visualized with reduced density gradient analysis (RDG). Finally, molecular docking was performed with Auto-Dock 4.2 to study the interactions between donors (DPSAMP or metallic complexes) and receptors [Escherichia coli (PDB code: 1HNJ) or Candida albicans (PDB code: 1H1W)].

Theoretical investigation of HER/OER/ORR catalytic activity of single atom-decorated graphyne by DFT and comparative DOS analyses

Multifunctional catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) play a key role in the development of electrochemical energy systems. Moreover, single metal atoms embedded in a two-dimensional material substrate have emerged as outstanding catalysts. Owing to its large surface area and novel electronic properties, graphyne (GY) is a promising substrate for the fabrication of single-atom catalysts (SACs). By doping foreign atoms of different types on GY, their local electronic/chemical environment and catalytic performance would be improved. Based on recent experimental advances, we used density functional theory (DFT) simulations to identify a suitable series of co-decorated GY materials, with boron-, nitrogen-, phosphorus-, and sulfur-doped GY (3B-GY, 3N-GY, 3P-GY, 3S-GY) as the two-dimensional substrate, and transition metal (TM) atoms (Sc to Zn) as the single-atom centers. Our screening process showed that Co@GY and Ni@3B-GY would be highly promising multifunctional electrocatalysts for HER/OER/ORR. Then, we built quantitative structure–property relationship (QSPR) between electronic density of states (DOS) structure and catalytic performance using comparative DOS analysis (CoDOSA). The present results further support the development and application of d-band center theory. Our work identifies promising co-decorated GY for HER/OER/ORR and provides quantitative information on their DOS.

DFT outcome for comparative analysis of Be12O12, Mg12O12 and Ca12O12 nanocages toward sensing of N2O, NO2, NO, H2S, SO2 and SO3 gases

The gas sensing applications of nanocages find intense attention in environmental monitoring. In this research, the adsorption of nitrogen and sulfur-containing gaseous molecules i.e., N2O, NO2, NO, H2S, SO2, and SO3 on inorganic oxide nanocages are analyzed through DFT simulations. The adsorption of gaseous molecules with Be12O12, Mg12O12, and Ca12O12 is illustrated through the adsorption energies, optimized geometries, and electronic properties like HOMO-LUMO energies and NBO analysis. Our theoretical analysis indicates that the molecules strongly bind with the Ca12O12 nanocage. The adsorption energies of N2O@Ca12O12, NO2@Ca12O12, NO@Ca12O12, H2S@Ca12O12, SO2@Ca12O12 and SO3@Ca12O12 are −11.79, −46.53, −26.51, −50.26, −78.64 and −123.62 kcal/mol, respectively. Moreover, the HOMO-LUMO orbital analysis, density of state analysis (DOS), and natural bond orbital (NBO) analysis illustrate the significant impact of adsorption of these molecules on the electronic properties of respective nanocages, especially Ca12O12. Finally, it can be concluded that the Ca12O12 nanocage shows promising sensitivity towards the gaseous molecules which is followed by Mg12O12 and Be12O12.

Dual-metal-organic frameworks as ultrahigh-performance bifunctional electrocatalysts for oxygen reduction and oxygen evolution

At present, it is significant to research bifunctional catalysts for metal-air batteries with bargain price, excellent stability, and satisfactory activity. Herein, by density functional theory, the performance of dual-metal-organic frameworks M2-BTC (M2 = Ni2, Fe2, Co2, FeNi, CoNi, FeCo) as bifunctional electrocatalysts to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is investigated. All M2-BTC are proved to possess satisfactory thermodynamical stability. For ORR, FeNi-Ni, Ni2-BTC, Co2-BTC, and CoNi-Ni are confirmed to have high activity with corresponding overpotential of 0.40, 0.25, 0.31, and 0.28 V, respectively, which are both better than Pt(111) (ηORR = 0.45 V). For OER, Fe2-BTC, Ni2-BTC, Co2-BTC, and CoNi-Ni show excellent catalytic activity, with the overpotential of 0.42, 0.38, 0.22, and 0.31 V, respectively, which can be compared to RuO2(110) (ηOER = 0.37 V) or even better than it. According to the ORR/OER potential gap, Ni2-BTC, Co2-BTC, and CoNi-Ni are screened out to be ultrahigh-performance bifunctional electrocatalysts. The results of the highest occupied molecular orbital and the lowest unoccupied molecular orbital confirm that the metal atom is the main active site, and the O atoms attached to the active metal also participate in the reaction. Density of states analysis indicates that the different catalytic performance of M2-BTC is caused by the variety of electronic structures.

First-principles investigations into the effect of oxygen vacancies on the enhanced reactivity of NiO via Bader charge and density of states analysis

Vacancy defects are important parameters in determining the reactivity of metal oxides. Different areas such as catalysis, fuel cell, battery, and other energy conversion technologies (e.g., chemical looping combustion) can benefit from fundamental studies on the effect of vacancy defects on metal oxide reactivity. The effect of oxygen vacancies on the reactivity of NiO, which is a prominent and promising material in the aforementioned areas, is studied in this work. Using density functional theory, a comprehensive analysis of oxygen vacancy effect on the hydrogen chemisorbed state of NiO (100) is provided with Bader charge, charge redistribution, and density of states analyses. By inclusion of an oxygen vacancy, adsorption sites change from Ni and O sites on NiO to O and O vacant sites on NiO1−x. Adsorbed hydrogen on the positively charged oxygen vacant site has an enhanced interaction with two neighboring Ni atoms. As revealed by our analysis, change in the magnitude of H–Ni interaction is the main contributor to the enhanced reactivity of NiO by the addition of O vacancy. The results establish an understanding of the enhanced reactivity by the creation of O vacancies and elucidate the changes in the bonding nature as a result of the vacancy.

Examining computationally the structural, elastic, optical, and electronic properties of CaQCl3 (Q = Li and K) chloroperovskites using DFT framework.

This study presents the investigations of structural, elastic, optical, and electronic properties of CaQCl3 (Q = Li and K) chloroperovskites for the first time using the DFT framework. The WIEN2K and IRelast packages are used in which the exchange-correlation potential of the modified Becke-Johnson potential (TB-mBJ) is used for obtaining better results. The optimized crystal structural parameters comprising the lattice constant, optimum volume, ground state energy, bulk modulus, and the pressure derivative of bulk modulus are computed by fitting the primitive unit cell energy versus primitive unit cell volume using the Birch-Murnaghan equation of state. The elastic properties which consist of cubic elastic constants, Poisson's ratio, elastic moduli, anisotropy factor, and the Pugh ratio are computed using the very precise IRelast package incorporated inside WIEN2K. The electronic properties are analyzed from the computation of electronic bands structure and density of states (DOS), and it is concluded that an indirect band gap of 4.6 eV exists for CaLiCl3 and a direct band gap of 3.3 eV for CaKCl3 which confirms that CaLiCl3 is an insulator while CaKCl3 is a wide band gap semiconductor. The analysis of DOS shows that the greater contribution to the conduction band (CB) occurs because of the "Ca" element whereas in the valence band the major contribution is from the "Cl" element. The spectral curves of various parameters of optical properties from 0 eV up to 42 eV incident photon energies are observed and it is found that the CaQCl3 (Q = Li and K) chloroperovskites are optically active having a high absorption coefficient, optical conductivity, optical reflectivity, and energy loss function from 25 eV to 35 eV incident photon energies. The applications of these materials can be deemed to alter or control electromagnetic radiation in the ultraviolet (UV) spectral regions. In summary, the results for selected CaQCl3 (Q = Li and K) chloroperovskites depict that these are important compounds and can be used as scintillators, and energy storage devices, and in many modern electronic gadgets.

First-Principles Study of Defected Single Layer Hexagonal Boron-Nitride (h-BN)

The novel properties of pristine h-BN, oxygen (O) atom impurity defects in h-BN (h-B(N-O) and h-(B-O)N), one boron (1B) atom vacancy defect in h-BN (h-BN_1B) and one nitrogen (1N) atom vacancy defect in h-BN (h-BN_1N) materials are investigated by spin-polarized density functional theory (DFT) using computational tool Quantum ESPRESSO. We found that they are stable materials. From the band structure calculations, we found that all the considered systems are wide bandgap materials. The bandgap energy of pristine h-BN, impurity defects h-B(N-O) and h-(B-O)N, and vacancy defects h-BN_1B and h-BN_1Nmaterials have values 4.98 eV, 4.19 eV&amp; 2.47 eV,and 4.84 eV&amp; 3.62 eV respectively. Also, it is found that h-B(N-O) and h-BN_1N materials have n-type Schottky contact while h-(B-O)N and h-BN_1B materials have p-type Schottky contact. From the analysis ofdensity of states (DOS) and partial density of states (PDOS) calculations, we found that non-magnetic pristine h-BN changes to magnetic h-B(N-O) andh-(B-O)N materials due to presence of impurity defects,and h-BN_1B andh-BN_1N materials due to presence of vacancy defects. Magnetic moments of h-B(N-O), h-(B-O)N, h-BN_1B and h-BN_1N materials are 1.00 µB/cell, 0.94 µB/cell, 3.00 µB/cell and 1.00 µB/cell respectively. They are obtained due to unpaired up and down spins state of electrons in 2p orbital of B and N atoms in the structures.

Adsorption and sensing performances of transition metal (Ag, Pd, Pt, Rh, and Ru) modified WSe2 monolayer upon SF6 decomposition gases (SOF2 and SO2F2)

In this study, we explored the adsorption of SF6 decomposition products (SOF2 and SO2F2) on transition metal (Ag, Pd, Pt, Rh, and Ru) modified WSe2 (with adatom and TM-substitution) using DFT calculations. The adsorption energy, charge transfer, electrostatic potential, and density of states of the adsorption structures between the target gas molecules and TM-WSe2 were studied. The calculation results show that the conductivity of the WSe2 monolayer modified with metal atoms is improved. And the adsorption energy of these gases on Ag-WSe2 (with adatom), and SO2F2 on Pd, Pt modified WSe2 (with TM-substitution) is very small. The density of states analysis indicates that Ag-WSe2 (with TM-substitution) shows weak sensing property to SO2F2 molecule. Therefore, these five modified systems are not suitable for gas-sensing equipment. For other modified systems, the conductivity decreases to different degrees after the adsorption of gas. Therefore, the gases can be detected according to the different change rule of conductivity after adsorption. In addition, these adsorption structures have a reasonable recovery time. The results not only have important significance for explaining the sensing mechanism of TM modified WSe2 adsorption to SF6 decomposition products, also provide a potential material for the further development of gas-sensing sensors.

New insights into NO adsorption on alkali metal and transition metal doped graphene nanoribbon surface: A DFT approach

The aim of this article is to investigate the sensing performance of NO gas molecule on the graphene nanoribbon domain for the determination of structural and electronic properties. Effect of an alkali metal (lithium) and a transition metal (iron) on the armchair oriented graphene nanoribbon (ArGNR) surface for the sensing purpose of NO gas has been performed through the quantum mechanics based Density Functional Theory (DFT) calculations. Various configurations of ArGNR doped with Li and Fe atoms such as one-edge doped, center doped, both-edge doped Li-ArGNR and Fe-ArGNR have been simulated, and a detailed comparative study of lithium and iron doping on different configurations of ArGNRs for the adsorption energy, stability analysis, band gap analysis and density of states analysis has been quantitatively evaluated. By comparing the adsorption energy of NO, it is found that Li doping enhances the strength of NO adsorption on the different variants of ArGNR. Computational results predict that the undoped ArGNR is insensitive to the NO gas adsorption with adsorption energy of about −0.41 eV. Our results determine that substitutional doping of Li doping at one edge doped and both-edge doped position increases the adsorption abilities of ArGNRs in these configurations with adsorption energies of approximately −6.92 eV and −9.64 eV that is 16 and 23 times greater than the pristine ArGNR (Pr-ArGNR). Band nature for both type of doping estimates the changing behavior of ArGNRs from semiconductor to metallic transition after the adsorption of NO molecule. It is concluded that the Li doping at one edge and both edge position of ArGNR makes it an excellent potential sensing material for the sensing purpose of NO gas as compared to the Fe doped configurations.

Structural evolution and phase transition mechanism of hbox {MoSe}_2 under high pressure

hbox {MoSe}_2 is a layered transition-metal dichalcogenide (TMD) with outstanding electronic and optical properties, which is widely used in field-effect transistor (FET). Here the structural evolution and phase transition of hbox {MoSe}_2 under high pressure are systematically studied by CALYPSO structural search method and first-principles calculations. The structural evolutions of hbox {MoSe}_2 show that the ground state structure under ambient pressure is the experimentally observed P6_3/mmc phase, which transfers to R3m phase at 1.9 GPa. The trigonal R3m phase of hbox {MoSe}_2 is stable up to 72.1 GPa, then, it transforms into a new P6_3/mmc phase with different atomic coordinates of Se atoms. This phase is extremely robust under ultrahigh pressure and finally changes to another trigonal R-3m phase under 491.1 GPa. The elastic constants and phonon dispersion curves indicate that the ambient pressure phase and three new high-pressure phases are all stable. The electronic band structure and projected density of states analyses reveal a pressure induced semiconducting to metallic transition under 72.1 GPa. These results offer a detailed structural evolution and phase diagram of hbox {MoSe}_2 under high pressure, which may also provide insights for exploration other TMDs under ultrahigh pressure.

Highly Efficient Doping of Conjugated Polymers Using Multielectron Acceptor Salts.

Chemical doping is a vital tool for tuning electronic properties of conjugated polymers. Most single electron acceptors used for p-doping necessitate high dopant concentrations to achieve good electrical conductivity. However, high-molar doping ratios hamper doping efficiency. Here a new concept of using multielectron acceptor (MEA) salts as dopants for conjugated polymers is presented. Two novel MEA salts are synthesized and their doping efficiency towards two polymers differing in their dielectric properties are compared with two single electron acceptors such as NOPF6 and magic blue. Cutting-edge methods such as ultraviolet photoelectron spectroscopy/X-ray photoelectron spectroscopy (XPS), impedance spectroscopy, and density of states analysis in addition to UV-vis-NIR absorption, spectroelectrochemistry, and Raman spectroscopy methods are used to characterize the doped systems. The tetracation salt improves the conductivity by two orders of magnitude and quadruples the charge carrier concentration compared to single electron acceptors for the same molar ratio. The differences in charge carrier density and activation energy on doping are delineated. Further, a strong dependency of the carrier release on the polymer polarity is observed. High carrier densities at reduced dopant loadings and improved doping efficacies using MEA dopants offer a highly efficient doping strategy for conjugated polymers.

Density Functional Theory Study on the Effect of Isomorphic Substitution of FAU Molecular Sieve on N2 Adsorption Performance

Low pressure and anoxia are the main characteristics of the environment in the Tibetan Plateau, which means people living there have a large demand for oxygen to reduce the symptoms of altitude sickness. Pressure swing adsorption (PSA) is a competitive oxygen production technology in plateau areas, which relies on the molecular sieves for the separation of N2 and O2 in industry and portable medical equipment. The adsorption characteristics of the Faujasite-type (FAU) molecular sieves, as one kind of the most widely used adsorbents for O2 production, depend on the properties, amount, and distribution of the skeleton cations and atoms. In this paper, we explore the isomorphic substitution effect on the adsorption properties of N2 in FAU molecular sieves using the computational approaches based on the density functional theory (DFT). The structural analysis and adsorption energy calculated for the Zn, Ca, and Ga substitutions at the Si/Al skeleton sites in the β-cage structure, the basic unit of FAU molecular sieves, prove that the isomorphic substitution effect can strengthen the adsorption of N2. The Bader charge and density of states analysis validate the formation of electron-deficient holes near the Fermi level and hence strengthen the local polarity of the pore structure and enhance the adsorption of N2 molecules. The work about isomorphic substitution on the FAU molecular sieves might provide an insight into heteroatom isomorphic modification mechanisms and designing excellent air separation materials.