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We have calculated the melting temperature of tungsten by two ab initio approaches. The first approach can be divided into two steps. In the first step, we simulate a large coexisting solid and liquid system by the classical embedded-atom method potential and obtain an approximate melting temperature. In the second step, we compute the accurate melting temperature by performing the ab initio free-energy corrections. The second approach is to perform a direct ab initio molecular-dynamics simulation for the coexisting solid and liquid system using the constant particle number, pressure, and enthalpy ensemble. In the second approach, the simulation is carried out entirely using a density-functional theory Hamiltonian, and no other approximations are imposed. However, the simulation is performed using a relatively small supercell. The results obtained from two ab initio approaches can provide a check for each other. Our results show that they are in good agreement with each other and also in reasonably good agreement with the experimental value.

Secondary cosmic ray fluxes are important probes of the propagation and interaction of high-energy particles in the Galaxy. Recent measurements of primary and secondary cosmic ray nuclei have revealed unexpected spectral features that demand a deeper understanding. In this work we report the direct measurement of the cosmic ray boron spectrum from $10\mathrm{GeV}/\mathrm{n}$ to $8\mathrm{TeV}/\mathrm{n}$ with eight years of data collected by the Dark Matter Particle Explorer (DAMPE) mission. The measured spectrum shows a hardening at $182\pm 24\mathrm{GeV}/\mathrm{n}$ with a spectral index of ${\gamma }_1=3.02\pm 0.01$ before the break and an index change of $\mathrm{\Delta }\gamma =0.31\pm 0.05$ after the break. A simple power law model is disfavored at a confidence level of $8\sigma$. Compared with the hardenings measured in the DAMPE proton and helium spectra, the secondary boron spectrum hardens roughly twice as much as these primaries, which is consistent with a propagation related mechanism to interpret the spectral hardenings of cosmic rays observed at hundreds of $\mathrm{GeV}/\mathrm{n}$.

We study the energetics of island formation in Stranski-Krastanow growth of highly mismatched heteroepitaxy within a parameter-free approach. It is shown that the (frequently found) rather narrow size distribution of the self-assembled coherent islands can be understood as the result of the system being trapped in a constrained equilibrium state with a fixed island density. If allowing for variations of the island density, we find that larger islands combined with a lower island density are more stable; this implies that Ostwald ripening will take place on time scales sufficiently long for exchange of atoms between different islands to occur. Moreover, we show how to select the island size by controlling the growth conditions and the amount of deposited material. Our study also indicates that the island shape depends on the island size, i.e., an island with larger volume has a higher value of the height-to-base ratio.

The present paper is the reply to Sandu’s Comment on our paper [Phys. Rev. B 72, 153314 (2005)], i.e., the effect of the current operator on the spin-dependent tunneling through a barrier in the presence of the Dresselhaus spin-orbit interaction (DSOI). We demonstrate theoretically and numerically that our previous numerical result is correct when there is no DSOI in the contact region and it remains a good approximation in the presence of the $k^3$-DSOI in the contact regions.

Investigation of the resident site and the adsorption phase structure of thiolates is of fundamental importance for understanding the formation of self-assembled organic monolayers on metal substrate surfaces. In the present study, we have investigated adsorption of methanethiol, ${\mathrm{CH}}_3\mathrm{SH}$, on the ferromagnetic $\mathrm{Co}\left(0001\right)$ surface using density functional theory calculations. We find that the dissociative adsorption of ${\mathrm{CH}}_3\mathrm{SH}$ forming an adsorbed methylthiolate $\left({\mathrm{CH}}_3\mathrm{S}\right)$ and an adsorbed $\mathrm{H}$ atom is energetically favorable, and that the ${\mathrm{CH}}_3\mathrm{S}$ molecule adsorbed at the threefold fcc and hcp hollow sites is most stable. The adsorption energy at the bridge site is only $\sim 0.2\mathrm{eV}$ smaller than that at the threefold hollow site, and the adsorption of ${\mathrm{CH}}_3\mathrm{S}$ at the atop site is unstable. For the $\left(\sqrt{3}\times \sqrt{3}\right)\mathrm{R}30°$, $\left(2\times 2\right)$ and $\left(2\times 3\right)$ adsorptions, we find that the $\mathrm{S}‐\mathrm{C}$ bond tends to be normal to the surface, whereas for the $\left(2\times 1\right)$ adsorption it tilts away from the surface normal direction by $\sim 40°$. The $\left(2\times 1\right)$ adsorption phase is much less stable. The reduction of the adsorption energy with the increasing coverage is attributed to the repulsive interaction between the adsorbates. Our calculations show that the $\left(\sqrt{3}\times \sqrt{3}\right)\mathrm{R}30°$ structure may form in the process of methylthiolate adsorption on $\mathrm{Co}\left(0001\right)$ due to its adsorption energy being only $0.1\mathrm{eV}$ lower than that for the $\left(2\times 2\right)$ and $\left(2\times 3\right)$ structures. We find that there is a charge transfer from the substrate surface atoms to the $\mathrm{S}$ atoms, and that the $\mathrm{S}‐\mathrm{Co}$ bond is strongly polar. The surface $\mathrm{Co}$ atoms bound to $\mathrm{S}$ have a magnetic moment of $\sim 1.66{\mu }_B$, while the surface $\mathrm{Co}$ atoms unbound to $\mathrm{S}$ have a larger magnetic moment of $\sim 1.85{\mu }_B$. The $\mathrm{S}$ atom in the adsorbed ${\mathrm{CH}}_3\mathrm{S}$ acquires a magnetic moment of $\sim 0.08{\mu }_B$.

The total-energy calculations using a full-potential first-principles method have been performed for three displacive phase transformation modes in Cu. The structural and elastic properties of the ground-state (fcc) and higher-energy phases (bcc and $9R)$, as well as the energy barrier for sliding of $\{111{\}}_{\mathrm{fcc}}$ close-packed atomic planes and the stacking fault energy were obtained. Stability of higher-energy phases in the region of extended defects is discussed in detail. Examples presented are bcc and $9R$ Cu in grain boundaries and bcc Cu in pseudomorphic films at low temperatures. It is shown that the higher-energy phases, which are usually unstable, can be stabilized in the region of extended defects by certain imposed constraints.

Spin-dependent tunneling through a symmetric semiconductor barrier is studied including the $k^3$ Dresselhaus effect. The spin-dependent transmission of an electron can be obtained analytically. By comparing with previous work [Phys. Rev. B 67, 201304(R) (2003) and Phys. Rev. Lett. 93, 056601 (2004)], it is shown that the spin polarization and interface current are changed significantly by including the off-diagonal elements in the current operator, and can be enhanced considerably by the Dresselhaus effect in the contact regions.

Nickel, one of the most tightly bound nuclei alongside iron, is the most abundant heavy element beyond iron in cosmic rays. With DAMPE’s excellent charge resolution and broad energy range, a high-precision energy spectrum provides valuable insights into the acceleration sources of heavy nuclei and their propagation through the interstellar medium. In this analysis, we report the direct measurement of cosmic-ray nickel spectrum from 10 GeV/n to 2 TeV/n with nine years of flight data. The nickel spectrum is consistent with a single power law with spectral index $-2.60\pm 0.03$ from 40 GeV/n to 1 TeV/n. This Letter provides an accurate measurement of differential flux of nickel with kinetic energy extending to TeV/n for the first time.

We discover that Au-rich ${\mathrm{C}\mathrm{u}}_{1-x}{\mathrm{A}\mathrm{u}}_x$ and Pt-rich ${\mathrm{N}\mathrm{i}}_{1-x}{\mathrm{P}\mathrm{t}}_x$ contain a composition range in which there is a quasicontinuum of stable, ordered “adaptive structures” made of (001) repeat units of simple structural motifs. This is found by searching $\sim 3\times {10}^6$ different fcc configurations whose energies are parametrized via a “cluster expansion” of first-principles-calculated total energies of just a few structures. This structural adaptivity is explained in terms of an anisotropic, long-range strain energy.

The phonon instabilities of cesium related to its pressure-induced $\mathrm{bcc}-\mathrm{to}-{\mathrm{fcc}}^{\mathrm{}\left(1\right)\mathrm{}}-\mathrm{to}-{\mathrm{fcc}}^{\mathrm{}\left(2\right)\mathrm{}}$ phase transitions are studied using the density-functional perturbation theory. It is found that at low pressure, both the bcc and fcc Cs are dynamically stable, but fcc is thermodynamically metastable. The high-pressure phase transitions of Cs from bcc to ${\mathrm{fcc}}^{\mathrm{}\left(1\right)\mathrm{}}$ and from ${\mathrm{fcc}}^{\mathrm{}\left(1\right)\mathrm{}}$ to ${\mathrm{fcc}}^{\mathrm{}\left(2\right)\mathrm{}}$ are related to the phonon instabilities of the long-wavelength acoustic modes resulted from the negative tetragonal shear elastic constant $C^{\prime }=\frac{1}{2}{(C}_{11}-C_{12}).\mathrm{}$ During the ${\mathrm{fcc}}^{\mathrm{}\left(1\right)\mathrm{}}-\mathrm{to}-{\mathrm{fcc}}^{\mathrm{}\left(2\right)\mathrm{}}$ phase transition, all the phonon modes become soft, making it the most striking feature of this isostructural phase transition.

Precise direct cosmic-ray (CR) measurements provide an important probe to study the energetic particle sources in our Galaxy, and the interstellar environment through which these particles propagate. Uncertainties on hadronic models, ion-nucleon cross sections in particular, are currently the limiting factor toward obtaining more accurate CR ion flux measurements with calorimetric space-based experiments. We present an energy-dependent measurement of the inelastic cross section of protons and helium-4 nuclei (alpha particles) on a ${\mathrm{Bi}}_4$${\text{Ge}}_3{\mathrm{O}}_{12}$ target, using 88 months of data collected by the DAMPE space mission. The kinetic energy range per nucleon of the measurement points ranges from 18 GeV to 9 TeV for protons, and from $5\mathrm{GeV}/\mathrm{n}$ to $3\mathrm{TeV}/\mathrm{n}$ for helium-4 nuclei. Our results lead to a significant improvement of the CR flux normalization. In the case of helium-4, these results correspond to the first cross section measurements on a heavy target material at energies above $10\mathrm{GeV}/\mathrm{n}$.

The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target. The measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with geant4 and fluka simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE’s cosmic-ray flux measurements.

Cd-rich CdSe nanocrystals below a critical size, under illumination, catalyze ${\mathrm{\text{CO}}}_2$ fixation, but bulk CdSe surfaces do not. We report first-principles calculations in which we determine the roles of faceting, deviations from stoichiometry, photoexcitation, and electron confinement, and the specific physics of the nanoscale. We further establish that catalysis does not occur at the nanocrystal surface; instead, neutral molecules adsorb, desorb negatively charged, and react elsewhere. Finally, we predict that $n$-type doped CdSe nanocrystals would be effective catalysts without photoexcitation.

Previous calculations on n-type doping of diamond by P and S predicted that S has a shallower level and a higher solubility than P. Our first-principles calculations show that the opposite is true: Phosphorus impurity in diamond gives rise to a shallower donor level, and has a higher bulk solid solubility than sulphur. This agrees with the trends expected from the strength of the atomic pseudopotentials. We predict that coherent epitaxial expansion would substantially increase the solubility of P, and that complex formation of P with H is exothermic, also leading to passivation of the P donor action; removal of H then is needed to achieve good n-type characteristicy.

We show that the existence of stable, ordered $3d-5d$ intermetallics CuAu and NiPt, as opposed to the unstable $3d-4d$ isovalent analogs CuAg and NiPd, results from relativity. First, in shrinking the equilibrium volume of the $5d$ element, relativity reduces the atomic size mismatch with respect to the $3d$ element, thus lowering the elastic packing strain. Second, in lowering the energy of the bonding $6s,p$ bands and raising the energy of the $5d$ band, relativity enhances (diminishes) the occupation of the bonding (antibonding) bands. The raising of the energy of the $5d$ band also brings it closer to the energy of the $3d$ band, improving the $3d-5d$ bonding.

Recent observations of the light component of the cosmic-ray spectrum have revealed unexpected features that motivate further and more precise measurements up to the highest energies. The Dark Matter Particle Explorer is a satellite-based cosmic-ray experiment that has been operational since December 2015, continuously collecting data on high-energy cosmic particles with very good statistics, energy resolution, and particle identification capabilities. In this work, the latest measurements of the energy spectrum of $\mathrm{proton}+\mathrm{helium}$ in the energy range from 46 GeV to 464 TeV are presented. Among the most distinctive features of the spectrum, a spectral hardening at 600 GeV has been observed, along with a softening at 29 TeV measured with a $6.6\sigma$ significance. Moreover, the detector features and the analysis approach allowed for the extension of the spectral measurement up to the sub-PeV region. Even if with small statistical significance due to the low number of events, data suggest a new spectral hardening at about 150 TeV.

The Forbush decrease of cosmic rays is an important probe of the interplanetary environment disturbed by solar activities. In this Letter, we study the properties of eight Forbush decreases’ electrons (including positrons) between 2 and 20 GeV from January 2016 to March 2024 with the Dark Matter Particle Explorer. The maximum decrease amplitudes of these events are about 30%–15%, and the amplitudes reduce with energy. The recovery time of these events shows diverse behaviors of their energy dependence. Some of them show strong energy dependence, while some have a nearly constant recovery time. It has been shown that such diverse behaviors could be related to the geometry of the regions of the interplanetary space disturbed by coronal mass ejections, which can be characterized by the combined effect of the coronal mass ejection velocity, angular spread, and ejection direction.

We study the energetics of island formation in Stranski-Krastanow growth within a parameter-free approach. It is shown that an optimum island size exists for a given coverage and island density if changes in the wetting layer morphology after the 3D transition are properly taken into account. Our approach reproduces well the experimental island size dependence on coverage and indicates that the critical layer thickness depends on growth conditions. The present study provides a new explanation for the (frequently found) rather narrow size distribution of self-assembled coherent islands.

More than a century after the performance of the oil drop experiment, the possible existence of fractionally charged particles (FCPs) still remains unsettled. The search for FCPs is crucial for some extensions of the Standard Model in particle physics. Most of the previously conducted searches for FCPs in cosmic rays were based on experiments underground or at high altitudes. However, there have been few searches for FCPs in cosmic rays carried out in orbit other than AMS-01 flown by a space shuttle and BESS by a balloon at the top of the atmosphere. In this study, we conduct an FCP search in space based on on-orbit data obtained using the Dark Matter Particle Explorer (DAMPE) satellite over a period of five years. Unlike underground experiments, which require an FCP energy of the order of hundreds of GeV, our FCP search starts at only a few GeV. An upper limit of $6.2\times {10}^{-10}{\mathrm{cm}}^{-2}{\mathrm{sr}}^{-1}{\mathrm{s}}^{-1}$ is obtained for the flux. Our results demonstrate that DAMPE exhibits higher sensitivity than experiments of similar types by three orders of magnitude that more stringently restricts the conditions for the existence of FCP in primary cosmic rays.

A dilute nonisovalent semiconductor alloy, made of a III-V semiconductor component (GaAs) mixed with a II-VI semiconductor (ZnSe), can be viewed as the doping of a host semiconductor with a lower (higher) valent cation and a higher (lower) valent anion. We have investigated different doping types, i.e., monodoping, triatomic codoping, and cluster doping, in the ZnSe-GaAs system using ab initio pseudopotential plane-wave calculations. We find the following: (i) The acceptor dopant clusters are stabilized in a chemical potential range different from that of the donor dopant clusters. This explains the experimental observation that a nonisovalent alloy has a distinct carrier polarity. (ii) Cluster doping, e.g., $(\mathrm{Zn}-{\mathrm{Se}}_4{)}^{3+}$ or $(\mathrm{Se}-{\mathrm{Zn}}_4{)}^{3-}$ in GaAs, is predicted to be stable at extreme chemical potential limits, and also to contribute free carriers. (iii) Triatomic codoping is predicted to be thermodynamically unstable. (iv) Cluster doping produces shallower acceptor/donor levels than monodoping and triatomic codoping. (v) There is a strong attractive interaction between positively charged donors and negatively charged acceptors. Therefore, a high concentration of the charge-neutral dopant pairs exists in the alloy. This finding explains why free carriers in a nonisovalent alloy have a high mobility. (vi) Our results also explain the asymmetric dependence of the band gap on the alloy composition. Specifically, adding a small amount of Ga+As into ZnSe leads to a sharp drop in the band gap of the host crystal, whereas adding Zn+Se into GaAs does not change the band gap very much.