Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equiv...Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equivalent-local complex potential.The s-wave resonances and the Wigner cusp feature at the positronium（n = 1） formation threshold are compared with the previous reports.The p-and the d-wave resonances and a Wigner cusp feature at the positronium（n = 2） formation threshold are reported for the first time.展开更多
The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and...The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and other theoretical calculation results.展开更多
We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical（CCO） method for incident energies below the H ionization thre...We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical（CCO） method for incident energies below the H ionization threshold. The target continuum and the positronium（Ps） formation channels are included in the coupled-channels calculations via a complex equivalent-local optical potential. The critical points, which show minima in the differential cross sections, as a function of the scattering angle and the incident energy are investigated. The resonances in the angular differential cross sections are reported for the first time in this energy range. The effects of the target continuum and the Ps formation channels on the different cross sections are discussed.展开更多
Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1...Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB_(12) are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB_(12) regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB_(12)(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB_(12) satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB_(12) should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.展开更多
The five longest tune-out wavelengths for the rubidium atom are predicted from existing experimental and theoretical information by using an approximation formula. The formula is derived from the analysis of a non- re...The five longest tune-out wavelengths for the rubidium atom are predicted from existing experimental and theoretical information by using an approximation formula. The formula is derived from the analysis of a non- relativistic configuration-interaction plus core polarization （CICP） calculation of the tune-out wavelengths for rubidium. The differences between the wavelengths predicted from the approximation formula and the exact CICP calculation are at the 10-3 nm level. The predicted five longest tune-out wavelengths are 790.115nm, 423.155nm, 421.111 nm, 359.429nm, and 359.022nm, respectively.展开更多
The low energy scattering of electrons by sodium at incident energies up to ionization threshold are calculated by applying the momentum space coupled-channel-optical （CCO） method. The present results are in good ag...The low energy scattering of electrons by sodium at incident energies up to ionization threshold are calculated by applying the momentum space coupled-channel-optical （CCO） method. The present results are in good agreement with the previous experimental and theoretical results. Furthermore, three resonances in the total cross sections observed by previous experiments are proved by the present calculation.展开更多
An approximation formula is developed to determine the tune-out wavelengths for the ground states of the alkalinemetal atoms lithium,sodium and cesium from the existing relativistic reduced matrix elements and experim...An approximation formula is developed to determine the tune-out wavelengths for the ground states of the alkalinemetal atoms lithium,sodium and cesium from the existing relativistic reduced matrix elements and experimental energies.The first longest tune-out wavelengths for Li,Na,and Cs are 670.971 nm,589.557 nm,and 880.237 nm,respectively.This is in good agreement with the previous high precise results of 670.971626 nm,589.5565 nm,and 880.25 nm from the relativistic all-order many-body perturbation theory（RMBPT） calculation[Phys.Rev.A 84 043401（2011）].展开更多
An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron- hydrogen resonances below the n = 2 excitation threshold. The equivalent local optical potential is used t...An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron- hydrogen resonances below the n = 2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated.展开更多
We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupledchannels optical method above the H (n =2) threshold.Resonances with angular momenta of L =0-6 are reported.I...We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupledchannels optical method above the H (n =2) threshold.Resonances with angular momenta of L =0-6 are reported.Ionization continuum and positronium formation channels are included via a complex equivalent local potential.Comparisons with the existing theoretical results are presented.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 10674055)
文摘Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equivalent-local complex potential.The s-wave resonances and the Wigner cusp feature at the positronium（n = 1） formation threshold are compared with the previous reports.The p-and the d-wave resonances and a Wigner cusp feature at the positronium（n = 2） formation threshold are reported for the first time.
文摘The direct ionization cross sections for electron scattering by nitrogen are calculated by applying an equivalentlocal optical model from 15eV to 1100eV. The present results are compared with the experimental data and other theoretical calculation results.
基金Project supported by the Nanyang Normal University Science Foundation of China(Grant No.ZX2013017)the National Natural Science Foundation of China(Grant Nos.11174066,61306007,and U1304114)
文摘We make a detailed study on the angular differential cross sections of positron–hydrogen collisions by using the momentum-space coupled-channels optical（CCO） method for incident energies below the H ionization threshold. The target continuum and the positronium（Ps） formation channels are included in the coupled-channels calculations via a complex equivalent-local optical potential. The critical points, which show minima in the differential cross sections, as a function of the scattering angle and the incident energy are investigated. The resonances in the angular differential cross sections are reported for the first time in this energy range. The effects of the target continuum and the Ps formation channels on the different cross sections are discussed.
基金Projected supported by the National Natural Science Foundation of China(Grant Nos.U1904179,U1904178,and 51501093)the Key Science Fund of Educational Department of Henan Province,China(Grant Nos.19A140013 and 20B140010)the Science Technology Innovation Talents Fund in Universities of Henan Province,China(Grant No.19HASTIT019)。
文摘Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB_(12)(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB_(12) are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB_(12) regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB_(12)(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB_(12) satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB_(12) should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11304063 and 11174066the Youth Foundation of Liaoning Normal University under Grant No LS2014L002
文摘The five longest tune-out wavelengths for the rubidium atom are predicted from existing experimental and theoretical information by using an approximation formula. The formula is derived from the analysis of a non- relativistic configuration-interaction plus core polarization （CICP） calculation of the tune-out wavelengths for rubidium. The differences between the wavelengths predicted from the approximation formula and the exact CICP calculation are at the 10-3 nm level. The predicted five longest tune-out wavelengths are 790.115nm, 423.155nm, 421.111 nm, 359.429nm, and 359.022nm, respectively.
文摘The low energy scattering of electrons by sodium at incident energies up to ionization threshold are calculated by applying the momentum space coupled-channel-optical （CCO） method. The present results are in good agreement with the previous experimental and theoretical results. Furthermore, three resonances in the total cross sections observed by previous experiments are proved by the present calculation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11304063 and 11174066)the Youth Foundation of Liaoning Normal University,China(Grant No.LS2014L002)
文摘An approximation formula is developed to determine the tune-out wavelengths for the ground states of the alkalinemetal atoms lithium,sodium and cesium from the existing relativistic reduced matrix elements and experimental energies.The first longest tune-out wavelengths for Li,Na,and Cs are 670.971 nm,589.557 nm,and 880.237 nm,respectively.This is in good agreement with the previous high precise results of 670.971626 nm,589.5565 nm,and 880.25 nm from the relativistic all-order many-body perturbation theory（RMBPT） calculation[Phys.Rev.A 84 043401（2011）].
基金Project supported by the National Natural Science Foundation of China(Grant No.10674055)
文摘An application of the coupled-channels optical method is given for the energy-dependent phenomena of positron- hydrogen resonances below the n = 2 excitation threshold. The equivalent local optical potential is used to account for the target polarization and positronium formation. The calculation includes 9 explicitly physical coupled channels. The lowest S-wave resonance energy position and new resonances are found. Angular dependence of the cross section in the resonance region are investigated.
基金Supported by the National Natural Science Foundation of China under Grant No 10674055.
文摘We investigate high partial wave resonances in positron-hydrogen scattering using the momentum-space coupledchannels optical method above the H (n =2) threshold.Resonances with angular momenta of L =0-6 are reported.Ionization continuum and positronium formation channels are included via a complex equivalent local potential.Comparisons with the existing theoretical results are presented.
