Effects of the Be_(22)W phase formation on hydrogen retention and blistering in mixed Be/W systems

We have performed first-principles density functional theory calculations to investigate the retention and migration of hydrogen in Be_（22） W, a stable low-W intermetallic compound. The solution energy of interstitial H in Be_（22） W is found to be 0.49 eV lower, while the diffusion barrier, on the other hand, is higher by 0.13 eV compared to those in pure hcp-Be. The higher solubility and lower diffusivity for H atoms make Be_（22） W a potential beneficial secondary phase in hcp-Be to impede the accumulation of H atoms, and hence better resist H blistering. We also find that in Be_（22） W, the attraction between an interstitial H and a beryllium vacancy ranges from 0.34 eV to 1.08 eV, which indicates a weaker trapping for hydrogen than in pure Be. Our calculated results suggest that small size Be_（22） W particles in hcp-Be might serve as the hydrogen trapping centers, hinder hydrogen bubble growth, and improve the resistance to irradiation void swelling, just as dispersed oxide particles in steel do.

Numerical simulations of strong-field processes in momentum space

The time-dependent Schr?dinger equation(TDSE)is usually treated in the real space in the textbook.However,it makes the numerical simulations of strong-field processes difficult due to the wide dispersion and fast oscillation of the electron wave packets under the interaction of intense laser fields.Here we demonstrate that the TDSE can be efficiently solved in the momentum space.The high-order harmonic generation and above-threshold ionization spectra obtained by numerical solutions of TDSE in momentum space agree well with previous studies in real space,but significantly reducing the computation cost.

First-principles study of He trapping in η-Fe_2C

The distribution of He in η-Fe2C has been studied by first-principles calculations.The formation energies of interstitial He and substitutional He（replacing Fe） are 3.76 eV and 3.49 eV,respectively,which are remarkably smaller than those in bcc Fe,indicating that He is more soluble in η-Fe2C than in bcc Fe.The binding potencies of both a substitutionalinterstitial He pair（1.28 eV） and a substitutional-substitutional He pair（0.76 eV） are significantly weaker than those in bcc Fe.The binding energy between the two He atoms in an interstitial-interstitial He pair（0.31 eV） is the same as that in bcc Fe,but the diffusion barrier of interstitial He（0.35 eV） is much larger than that in bcc Fe,suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe2C than in bcc Fe.Thus,self-trapping of He in η-Fe2C is less powerful than that in bcc Fe.As a consequence,small and dense η-Fe2C particles in ferritic steels might serve as scattered trapping centers for He,slow down He bubble growth at the initial stage,and make the steel more swelling resistant.