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Based on the k·p model, at a small constant energy surface, the Rashba spin splitting has a linear relationship with momentum k, while Hexagonal warping effect and a nonzero spin projection component Sz arise at a larger constant energy surface due to nonlinear k3 terms.

The magnetothermal properties and spintronic properties can be controlled by adjusting the carrier concentration and external magnetic field.

Accurate effective mass via precise 3D-band calculations of two new 2D semiconductors Bi2SSe2 and Bi2S2Se with high optical absorption.

The newly modeled ScSeCl and ScSeBr monolayers are promising photocatalysts for water splitting with high carrier mobilities.

Schematic of the photocatalytic water splitting of AlXY (X = S, Se and Y = Cl, Br, I) monolayers.

Janus transition metal dichalcogenide monolayers (TMDs) have attracted wide attention due to their unique physical and chemical properties since the successful synthesis of the MoSSe monolayer. However, the related studies of Janus monolayers of transition metal halides (TMHs) with similar structures have rarely been reported. In this article, we systematically investigate the electronic properties, piezoelectric properties, optical properties, and carrier mobility of new Janus TiXY (X ≠ Y, X/Y = Cl, Br, I) monolayers using first principles calculations for the first time. These Janus TiXY monolayers are thermally, dynamically, and mechanically stable, and their energy bands near the Fermi level (

Accumulating evidences have suggested that exosomes are closely associated with tumor progression by affecting cell‐cell communication. Here, we aimed to investigate the roles and regulatory mechanism of exosomes released from chronic lymphocytic leukemia (CLL). The expression levels of genes and proteins in cells and exosomes were examined by quantitative real‐time PCR and Western blotting, respectively. MEC‐1 cell‐derived exosomes were obtained and co‐cultured with human umbilical vein endothelial cells (HUVECs), then the capabilities of cell proliferation, metastasis and angiogenesis of HUVECs were measured by CCK‐8, wound healing, transwell and tube formation assay, respectively. Chloride intracellular channel 1 (CLIC1) was significantly increased in CLL patients and markedly enriched in exosomes secreted by CLL cells. Exosomal CLIC1 secreted from MEC‐1 cells were successfully transferred into HUVECs and significantly promoted the phenotypes of proliferation, metastasis and angiogenesis of HUVECs. Mechanically, exosomal CLIC1 secreted from MEC‐1 cells obviously activated MAPK/ERK signaling through upregulating integrin β1 (ITGβ1) expression in HUVECs. Furthermore, rescue experiments revealed that either silencing ITGβ1 or PD98059 treatment obviously reversed the regulatory effects of exosomal CLIC1 secreted from MEC‐1 cells in HUVECs. In conclusion, CLL cell‐derived exosomes accelerated HUVECs metastasis and angiogenesis through transferring CLIC1 to regulate ITGβ1‐MAPK/ERK signaling, indicating that CLIC1 may be a therapeutic target of CLL exosomes in the tumor microenvironment.

We here report a new pentagonal network structure of the PtM2 (M = S, Se, Te) monolayers with the P21/c (no. 14) space group. The electronic structure and thermoelectric properties of the pentagonal PtM2 monolayers are calculated through the VASP and BoltzTraP codes. We verify their dynamic and thermodynamic stabilities by calculating their phonon spectra and simulating ab initio molecular dynamics. It is found that the new material belongs to the medium-wide indirect band gap semiconductors from the PBE and HSE06 methods. At 300 K, the lattice thermal conductivities (Kl) of the pentagonal PtTe2 in the x and y directions are the smallest among these three materials, being 1.77 and 5.17 W/m K, respectively. The anisotropic zT values (2.60/1.14) in the x/y direction of the pentagonal PtTe2 at 300 K are much greater than those of the pentagonal PtSe2 (1.75/0.82) and the pentagonal PtS2 (0.58/0.16) at 300 K. Importantly, the p-type pentagonal PtTe2 also has excellent thermoelectric properties at 600 K, with a zT value of 5.03 in the x direction, indicating that the p-type pentagonal PtTe2 has a good application potential in the thermoelectric field.

Piezoelectric and thermoelectric materials that can directly convert mechanical and thermal energy into electricity have attracted great interest because of their practical applications in overcoming the challenges of the energy crisis. In this research, a new family of two-dimensional (2D) group-VI Janus ternary compounds with α and γ phases are predicted. After the stability testing, only the α-TeSSe monolayer has dynamic and thermal stability. The band structure and the optic, piezoelectric, and thermoelectric performances of the Janus α-TeSSe monolayer are calculated via the first-principles calculations. Janus α-TeSSe is a narrow indirect bandgap semiconductor with a value of 0.953 eV at HSE06 functional considering the spin-orbit coupling (SOC), which is beneficial to its thermoelectric performance, and its excellent absorption coefficients indicate that it may be a promising optoelectronic material. The piezoelectric calculations show that Janus α-TeSSe exhibits not only appreciable in-plane piezoelectricity (d11 = 17.17 pm/V ) but also superior vertical piezoelectricity (d31 = 0.22 pm/V). Furthermore, a new TansOpt code is used to calculate the electrical transport coefficients with a constant electron-phonon coupling approximation, which is more accurate than the constant relaxation time approximation. The origin of ultralow lattice thermal conductivity is also discussed in detail. Finally, ultrahigh ZT values of 0.77 and 1.95 occur in n-type and p-type doping at 600 K, respectively, indicating it is a promising thermoelectric material. Our work demonstrates that Janus α-TeSSe monolayers have potential applications in optoelectronic, piezoelectric, and thermoelectric devices, which will greatly stimulate research-related experiments.

The particle swarm optimization algorithm and density functional theory (DFT) are extensively performed to determine the structures, phase transition, mechanical stability, electronic structures, and thermodynamic properties of lanthanide phosphates (LaP and LaAs) in the pressure range of 0 to 100 GPa. Two novel high-pressure structures of LaP and LaAs are first reported here. It is found that LaX (X = P, As) undergo a phase transition from NaCl-type structure (Fm3m) to CsCl-type structure (P4/mmm) at 19.04 GPa and 17.22 GPa, respectively. With the elevation of the pressure, C2/m-LaP and Imma-LaAs are the most stable structures up to 70.08 GPa and 85.53 GPa, respectively. Finally, the analysis of the elastic constants and hardness confirms that the C2/m-LaP possesses hardness values up to 23.24 GPa due to the strong covalent P–P bonding and ionic La–P bonding, indicating that it is a potential hard material.

Studying the physical properties of materials under high pressure and temperature through experiments is difficult. Theoretical simulations can compensate for this deficiency. Currently, large-scale simulations using machine learning force fields are gaining popularity. As an important nuclear energy material, the evolution of the physical properties of uranium under extreme conditions is still unclear. Herein, we trained an accurate machine learning force field on alpha-U and predicted the lattice dynamics and elastic properties at high pressures and temperatures. The force field agrees well with the ab initio molecular dynamics (AIMD) and experimental results, and it exhibits higher accuracy than classical potentials. Based on the high-temperature lattice dynamics study, we first present the temperature-pressure range in which the Kohn anomalous behavior of the ${\Sigma}$4 optical mode exists. Phonon spectral function analysis showed that the phonon anharmonicity of alpha-U is very weak. We predict that the single-crystal elastic constants C44, C55, C66, polycrystalline modulus (E,G), and polycrystalline sound velocity ($C_L$,$C_S$) have strong heating-induced softening. All the elastic moduli exhibited compression-induced hardening behavior. The Poisson's ratio shows that it is difficult to compress alpha-U at high pressures and temperatures. Moreover, we observed that the material becomes substantially more anisotropic at high pressures and temperatures. The accurate predictions of alpha-U demonstrate the reliability of the method. This versatile method facilitates the study of other complex metallic materials., Comment: 21 pages, 9 figures, with Supplementary Material

We investigate the electronic structure, mechanical properties and thermal transport properties of ThC based on density functional theory. We find that thorium monocarbide shows metallic and mechanically stable at ground state, and the 5f-orbital and 6d-orbital electrons of Th atoms do not exhibit strong correlation properties. The Debye temperature obtained from the elastic constant is also in good agreement with the results of others. The thermal transport properties of ThC were discussed with the Boltzmann transport equation. It is found that the thermal conductivity of the lattice comes from the contribution of the acoustic support, and the optical branch has a lower thermal conductivity because of the suppression of the anharmonicity. The Seebeck coefficient and the power factor of ThC have a maximum at the valence band and increase with the increasing temperature, while the conductivity is less affected by the temperature. The electronic thermal conductivity increases with the increasing temperature, and at high temperatures, Widman-Franz law is ineffective. At low temperatures, the total thermal conductivity mainly comes from the lattice thermal conductivity; electrons occupy a major role at high temperatures. The thermoelectric figure of ThC is close to 0 at room temperature and cannot be used as a good thermoelectric material.

A thorough study on the thermal transport properties of the semimetal ScSb is carried out by combining first-principles calculations with Boltzmann transport theory. The dynamic stability of ScSb is verified by the phonon dispersion curve without an imaginary part. The obtained equilibrium lattice constant and bulk modulus agree well with the experimental and theoretical data. At room temperature, the calculated lattice thermal conductivity of ScSb is 29.9 W m−1 K−1, which is greatly larger than that of LaP (3.19 W m−1 K−1) due to its higher group velocity and smaller average Gruneisen parameter. By analyzing the contribution of each phonon mode to the lattice thermal conductivity, we find that the acoustic branch plays a dominant role, while the optical branch has little effect on it because of the inhibition of the anharmonicity. The temperature-dependent electronic transport properties, such as Seebeck coefficient, electrical conductivity, power factor, and thermal conductivity, as a function of chemical potential, are also investigated. It is shown that the electronic thermal conductivity increases with the increasing temperature and chemical potential. By comparing the temperature dependence of lattice thermal conductivity and electronic thermal conductivity, it is found that the lattice thermal conductivity is dominant in the low-temperature region and the electronic thermal conductivity is dominant in the high-temperature region. The calculated maximum figure of merit ZT of ScSb is only 0.044 at 900 K. Therefore, for the thermoelectric application of ScSb, it is necessary to improve the correlated parameters in other ways.

The design and search for efficient thermoelectric materials that can directly convert waste heat into electricity have been of great interest in recent years since they have practical applications in overcoming the challenges of global warming and the energy crisis. In this work, two new two-dimensional 1T-phase group-VI binary compounds Se

Topological semimetals have attracted significant attentions owing to their potential applications in numerous fields such as low-power electron devices and quantum computation, which are closely related to their thermal transport properties. In this work, the phonon transport properties of topological Dirac nodal-line semimetals ZrGe

Shock reverberation compression experiments on dense gaseous deuterium-helium mixtures are carried out to provide thermodynamic parameters relevant to the conditions in planetary interiors. The multishock pressures are determined up to 120 GPa and reshock temperatures to 7400 K. Furthermore, the unique compression path from shock-adiabatic to quasi-isentropic compressions enables a direct estimation of the high-pressure sound velocities in the unexplored range of 50--120 GPa. The equation of state and sound velocity provide particular dual perspectives to validate the theoretical models. Our experimental data are found to agree with several equation of state models widely used in astrophysics within the probed pressure range. The current data improve the experimental constraints on sound velocities in the Jovian insulating-to-metallic transition layer.

We systematically reported some properties of the AsSBr monolayer about the electronic structure, lattice thermal conductivity, thermal transport properties and thermoelectricity. There is no imaginary frequency in phonon dispersion, indicating that the AsSBr monolayer is dynamically stable. It is found the AsSBr monolayer is an indirect bandgap semiconductor with the bandgap 1.47 eV and 2.07 eV at PBE and HSE06 levels, respectively. For the first time, the lattice thermal conductivity KL of the AsSBr monolayer is calculated to be 1.34 W/m K at 300K. To reveal the origin of lower lattice thermal conductivity, the group velocity, scattering rate, and Gruneisen parameter γ are discussed. Combined with the calculated thermal transport properties, the ZT values at temperatures ranging from 300K to 900K are obtained. At 900K, the optimal ZT value of the p-type AsSBr monolayer is 0.91, indicating that the p-type AsSBr monolayer has prominent application in the thermoelectric field.

Weyl semimetal, a newly developed thermoelectric material, has aroused much interest due to its extraordinary transport properties. In this work, the thermoelectric transport properties of NbX (X = P and As), a prototypical Weyl semimetal, are investigated using the first-principles calculations together with Boltzmann transport theory. The calculated room-temperature lattice thermal conductivities along the a and c directions are 2.0 W mK−1 and 0.6 W mK−1 for NbP and 1.4 W mK−1 and 0.4 W mK−1 for NbAs, respectively. The low thermal conductivities may be useful in the thermoelectric applications. It is found that the acoustic branches have obvious contribution to the total lattice thermal conductivity, and the size dependence of the thermal conductivities can provide guidance for designing thermoelectric nanostructures. Our results show that the anisotropic structures of these compounds bring about the anisotropy of transport coefficients along the a and c directions, and the preferred direction is the c direction in thermoelectric applications. Moreover, NbP and NbAs show high ZT values of 0.82 and 0.50 along the c direction for p-type at an optimal carrier concentration, indicating that they are potential thermoelectric materials.

The design and search for efficient thermoelectric materials that can directly convert waste heat into electricity have been of great interest in recent years since they have practical applications in overcoming the challenges of global warming and the energy crisis. In this work, two new two-dimensional 1T-phase group-VI binary compounds Se2Te and SeTe2with outstanding thermoelectric performances are predicted using first-principles calculations combined with Boltzmann transport theory. The dynamic stability is confirmed based on phonon dispersion. It is found that the spin-orbit coupling effect has a significant impact on the band structure of SeTe2, and induces a transformation from indirect to direct band gap. The electronic and phononic transport properties of the Se2Te and SeTe2monolayer are calculated and discussed. High carrier mobility (up to 3744.321 and 2295.413 cm2V-1S-1for electron and hole, respectively) is exhibited, suggesting great applications in nanoelectronic devices. Furthermore, the maximum thermoelectric figure of meritzTof SeTe2for n-type and p-type is 2.88, 1.99 and 5.94, 3.60 at 300 K and 600 K, respectively, which is larger than that of most reported 2D thermoelectric materials. The surprising thermoelectric properties arise from the ultralow lattice thermal conductivitykl(0.25 and 1.89 W m-1K-1for SeTe2and Se2Te at 300 K), and the origin of ultralow lattice thermal conductivity is revealed. The present results suggest that 1T-phase Se2Te and SeTe2monolayer are promising candidates for thermoelectric applications.

We have carried out first-principles calculations on structural, electronic, carrier mobility and thermal transport properties of monolayer SrFBr. The dynamic, energetic, mechanical and thermodynamic stability of monolayer SrFBr is all confirmed. It is found that the monolayer SrFBr processes a direct bandgap of 5.23 eV (6.41 eV) obtained by PBE (HSE06), larger than many other 2D materials, and the wide bandgap of monolayer SrFBr can be regulated effectively by strain conditions. Along x and y directions, carrier mobility exhibited a maximum of 471 cm2 V−1· s−1. The lattice thermal conductivity obtained is 1.20 W m−1 K−1 at room temperature, which is lower than many other 2D materials. Additionally, we also obtain the related thermal properties, including group velocity, scattering rates, Gruneisen parameter and the volume of phase space, to explore the reason of the low thermal conductivity.

Janus monolayer materials have been extensively and systematically investigated since the successful synthesis of MoSSe monolayer which broke the out-of-plane mirror symmetry of TMDs monolayers. In order to explore the new Janus material, we turn our attentions to the family of halogens next to group-VIA (S, Se, Te) and carried out a systematic study of the ZrBrCl monolayer. By applying biaxial strain to ZrBrCl monolayer, the band gap of ZrBrCl monolayer changes from indirect to direct and then to indirect. In addition, the real and imaginary parts of the dielectric function and the absorption coefficient are calculated, which show the red shift under strain. It is found that the absorption range and strength in the visible region are almost the same as MoSSe monolayer, indicating that ZrBrCl monolayer may be a potential water-splitting photocatalyst. Moreover, we calculate that the lattice thermal conductivity of ZrBrCl monolayer at 300 K was 11.24 Wm−1K−1, and find that it is lower than that of MoSSe monolayer but slightly higher than that of ZrSSe monolayer. The reasons are analyzed through the phonon group velocity and phonon lifetime.

We studied the electronic structure and thermoelectric properties of SrO under pressure via first-principle calculations. The obtained phase transition pressure of SrO from B1 phase to B2 phase is 37 GPa at room temperature. At Gamma point, the phonon largest peak frequencies of SrO are 14.6 THz (B1 phase) and 18.9 THz (B2 phase), in addition, the LO-TO splitting frequencies are 8.6 THz (B1 phase) and 8.21 THz (B2 phase) under 0 GPa for B1 phase and 64 GPa for B2 phase, respectively. The B1 phase of SrO has an indirect band gap (3.31 eV) at 0 GPa, while the B2 phase has a smaller direct band gap (2.27 eV) at 70 GPa. At 0 GPa, the born effective charges of SrO are 2.44 (B1 phase) and 2.60 (B2 phase), and the dielectric constants are 3.80 (B1 phase) and 4.47 (B2 phase). When the temperature reaches 700 K and the carrier density reaches 1.2 × 10 21 cm−3, the ZT value of B1 phase reaches 0.61 at 0 GPa. By comparison, we found that the thermoelectric properties of the B1 phase behave better than those of the B2 phase at zero pressure.

Topological semimetals have attracted significant attentions owing to their potential applications in numerous fields such as low-power electron devices and quantum computation, which are closely related to their thermal transport properties. In this work, the phonon transport properties of topological Dirac nodal-line semimetals ZrGeX (X = S, Se, Te) with the PbClF-type structures are systematically studied using the first-principles calculations combined with the Boltzmann transport theory. The obtained lattice thermal conductivities show an obvious anisotropy, which is caused by the layer structures of ZrGeX (X = S, Se, Te). The room-temperature lattice conductivity of ZrGeTe along c direction is found to be as low as 0.24 W m−1 K−1, indicating that it could be of great significance in the fields of thermal coating materials and solar cell absorber. In addition, we extract each phonon branch from group velocities, phonon scattering rates, Grüneisen parameters, and phase space volumes to investigate the mechanism underlying the low thermal conductivity. It is concluded that the difference of thermal conductivities of three materials may be caused by the number of scattering channels and the effect of anharmonic. Furthermore, the phonon mean free path along a direction is relatively longer. Nanostructures or polycrystalline structures may be effective to reduce the thermal conductivity and improve the thermoelectric properties.

In this paper, the thermoelectric (TE) properties of Janus MXY monolayers (M = Pd, Pt; X, Y = S, Se, Te) are systematically studied using first principles and the Boltzmann transport theory. The thermal conductivity (k), Seebeck coefficient (S), power factor (PF), and TE figure of merit (ZT) are calculated accurately for various carrier concentrations. The lattice thermal conductivities of these six materials sequentially decrease in the order PtSSe, PtSTe, PtSeTe, PdSSe, PdSTe, and PdSeTe. PdSeTe and PtSeTe monolayers have a high ZT close to one at 300 K. In addition, we predicted the TE properties at high temperatures and found that the maximum ZT (2.54) is achieved for a monolayer of PtSeTe at 900 K. The structural and electronic properties of these six Janus transition-metal dichalcogenide (TMD) monolayers were systematically studied from first principles. Our results show that all six materials are semiconductors with bandgaps between 0.77 eV and 2.26 eV at the Heyd-Scuseria-Ernzerhof (HSE06) level. The present work indicates that the Janus MXY TMD monolayers (M = Pd, Pt; X, Y = S, Se, Te) are potentially TE materials.

Thermoelectric materials are attracting increasing attention for their ability to convert heat into cleaner electricity. In this work, we have systematically studied the thermoelectric properties of strontium sulfide (SrS) in the rock-salt structure based on first-principle calculations together with Boltzmann transport theory. The phonon spectra of the rock-salt structure SrS have no imaginary frequency modes, indicating the dynamic stability of SrS. The room-temperature lattice thermal conductivity κι of SrS is calculated to be 10.70 W/mK. We also calculated the phonon-mode contribution to κι, scattering rate, and mean free path (MFP). It is found that the acoustic branches have obvious contribution to the total lattice thermal conductivity, and the MFP can provide guidance for designing thermoelectric nanostructures. The ZT values of SrS with respect to carrier concentration n and temperature T are also obtained. It is found that, when temperature is from 300 K to 700 K, for p-type, the highest ZT value calculated by PBE varies from 0.15 to 0.41, and the highest ZT value by HSE varies from 0.10 to 0.30; For n-type, the highest ZT value by PBE varies from 0.08 to 0.26, and the highest ZT value by HSE varies from 0.09 to 0.28. In general, the p-type SrS has the better thermoelectric property than the n-type SrS.