Enhanced thermoelectric performance in Sb–Br codoped Bi2Se3 with complex electronic structure and chemical bond softening

A detailed description of the charge density difference of BiSb(Se0.92Br0.08)3.

Reconstruction and electronic properties of β-Li3PS4 |Li2S interface

The morphology and properties of the interface between solid electrolyte and electrode have important impacts on all-solid-state lithium-sulfur batteries’ performance. We used the first-principles calculations to explore the interface between Li2S cathode and β-Li3PS4 (lithium thiophosphate, LPS) solid electrolyte, including lattice structure, mechanical, electrical properties, interface contact type, and charge distribution in real space. It is found that the interface is significantly reconstructed, and the Li atoms at the interface move mainly parallel to the interface plane. The interface density states introduce metallic properties, mainly contributed by the Li-s and S-s, -p orbitals in Li2S and S-p orbitals in LPS. The highest occupied molecular orbitals of the LPS electrolyte are lower than the electrochemical potential (Fermi level) of the Li2S cathode, thus the electrolyte and cathode materials are reasonable and stable in thermodynamics. Interface density of states shows electrons on the interface do not penetrate from Li2S into LPS, and do not leak electrons to cause electron conduct in LPS. Besides, the interface is an n-type Schottky barrier with a barrier value of 1.0 eV. The work-function of the interface indicates that there is a space charge layer by the redistribution of electrons, which is in agreement with the result of interface charge density difference. The electron/hole pairs will be separate, realizing high current charge and discharge capability because of the space charge layer.

Structural Stability, Elasticity, Thermodynamics and Electronic Structures of L12-Type Ni3X (X=Al, Ti, V, Nb) Phases Under External Pressure Condition

In this paper, the impacts of external pressure on structural stability, elasticity, thermodynamics and relevant electronic structures of L12-type Ni3X (X=Al, Ti, V, Nb) phases were investigated using the first-principles methods. The lattice parameters(a,b,c) and volume(V) of the Ni3X phases decrease with increasing pressure. however, the elastic constants(Cij ), bulk modulus(B), shear modulus(G), and Young's modulus (E) increase. The calculated elastic constants indicate that the mechanical stability and ductility of Ni3X phases enhance with increasing pressure. The mechanical anisotropy of Ni3X phases are enhanced by the raised pressure. Electronic analysis shows that increase pressure makes Ni-d-orbital and X(X=Al, Ti, V, Nb) -d-orbital hybridization stronger and electron transfer increases. The sequence in regard to electron aggregation strength is Ni3Ti>Ni3Nb>Ni3V>Ni3Al. It is more directly reflected in the charge density difference maps. This is consistent with the analysis results of the enthalpy of formation(ΔH) and Debye temperature (ΘD).

First-Principles Study on Graphene/Mg2Si Interface of Selective Laser Melting Graphene/Aluminum Matrix Composites

The bonding strength of a Gr/Mg2Si interface was calculated by first principles. Graphene can form a stable, completely coherent interface with Mg2Si. When the (0001) Gr/(001) Mg2Si crystal plane is combined, the mismatch degree is 5.394%, which conforms to the two-dimensional lattice mismatch theory. At the interface between Gr/Mg2Si, chemical bonds were not formed, there was only a strong van der Waals force; the interfaces composed of three low index surfaces (001), (011) and (111) of Mg2Si and Gr (0001) have smaller interfacial adhesion work and larger interfacial energy, the interfacial energy of Gr/Mg2Si is much larger than that of α-Al/Al melt and Gr/Al interfacial (0.15 J/m2, 0.16 J/m2), and the interface distance of a stable interface is larger than the bond length of a chemical bond. The interface charge density difference diagram and density of states curve show that there is only strong van der Waals force in a Gr/Mg2Si interface. Therefore, when the Gr/AlSi10Mg composite is stressed and deformed, the Gr/Mg2Si interface in the composite is easy to separate and become the crack propagation source. The Gr/Mg2Si interface should be avoided in the preparation of Gr/AlSi10Mg composite.

Stability, Elastic and Electronic Properties of Ta2N by First-Principles Calculations

Owing to exploring the influence of the N atoms ordering in Ta2N compounds on their properties, the stability, elastic, and electronic properties of Ta2N compounds (Ta2N-I: P3¯ml and Ta2N-II: P3¯1m) were investigated using first-principles calculations based on density functional theory. Ta2N-II is energetically favorable according to the enthalpy of formation. Elastic constants were employed to reveal the stronger resistance to deformation, but weaker anisotropy, in Ta2N-II. A ductile-brittle transition was found between Ta2N-I (ductile) and Ta2N-II (brittle). The partial density of states showed a stronger orbital hybridization of Ta-d and N-p in Ta2N-II, resulting in stronger covalent bonding. The charge density difference illustrated the interaction of the Ta-N bond and electron distribution of Ta2N.

First-principles Investigation on the Electrical and Structural Characteristics of VO2 (M) and VO2 (R)

VO2 is promising sensing material for gas selection, and it has appealed to great attention. The structures of VO2 (M) and VO2 (R) crystal have been studied through the first principles. We investigated band structure, the density of states (DOS) and charge density difference of phases of VO2, the results show that when VO2 (M) is transformed into VO2 (R), the structure changes from semiconductor to conductor. The special property is expected to be used in gas sensors, lithium batteries, catalysis, supercapacitors and other fields. The basic findings of this calculation will be conducive to better comprehending of the characteristics and performance of VO2 crystal as a gas sensor material.

Heterofullerene MC59 (M = B, Si, Al) as Potential Carriers for Hydroxyurea Drug Delivery

As a representative nanomaterial, C60 and its derivatives have drawn much attention in the field of drug delivery over the past years, due to their unique geometric and electronic structures. Herein, the interactions of hydroxyurea (HU) drug with the pristine C60 and heterofullerene MC59 (M = B, Si, Al) were investigated using the density functional theory calculations. The geometric and electronic properties in terms of adsorption configuration, adsorption energy, Hirshfeld charge, frontier molecular orbitals, and charge density difference are calculated. In contrast to pristine C60, it is found that HU molecule is chemisorbed on the BC59, SiC59, and AlC59 molecules with moderate adsorption energy and apparent charge transfer. Therefore, heterofullerene BC59, SiC59, and AlC59 are expected to be promising carriers for hydroxyurea drug delivery.

Effect of B, Al, Ga doping on the electronic structure and optical property of 4H-SiC system by the first principles calculation

In this paper, the microscopic electronic structure and related optical properties of the 4H-SiC (111) surface doped with B, Al, Ga elements are explored by first principles calculation methods. Compared with Al- and Ga-doped systems, the formation energy of B-doped system is found to be very small, showing excellent stability. The bandgaps of doped system decrease obviously, and an indirect bandgap is observed in all the systems. Charge density difference maps show that the covalency is increased after B doping and the iconicity is increased after Al and Ga doping. Moreover, due to the sharp increase in static dielectric constant and dielectric loss, the B-doped system can be used as the candidate for absorbing materials. In addition, the increase in the peak value of the absorption and reflectivity makes the doped systems more promising in the development of solar cells.

Enhancing Charge Transfer and Photoelectric Characteristics for Organic Solar Cells

The main purpose of this work is to analyze the effect of steric hindrance on the photoelectric performance of three different donor sensitizers (ZHG5, ZHG6, and ZHG7) by molecular theory simulation engineering. Photoelectric physical and photoelectric chemical parameters are investigated by means of frontier molecular orbital, global reactivity descriptors, optical absorption properties, fluorescent lifetime, charge density difference, and influence of external electric field. The results showed that the performance of the quinoxaline sensitizer was deteriorated by gradually increasing the steric hindrance to auxiliary donors. The optical properties of the hybridization of cir-coronene graphene quantum dot (GR) with the three dyes have been revealed, and the results show that graphene quantum dots can indeed improve the optical properties of solar cells. In addition, nine new molecules were designed by inserting six functional groups; it is found that inserting -CN in the acceptor part of the molecular structure is beneficial to the performance of the sensitizer.