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First-principles calculations have been executed to investigate the interaction between H/He impurities and vacancy in tetragonal Be 12 Ti. The solution energies of four types of most stable H 1 V complexes are lower than that of He 1 V complexes. The binding energies of H atom to four types of vacancies are all lower than that of He atom to vacancies, indicating that He-vacancy complexes can serve as a trap to capture other impurity atoms. Besides, the formation energies of vacancy decrease when a single H or He atom is implanted into vacancy space, and the influence of He atom is greater than that of H atom. The exist of He atom in the H m HeV complexes leads to the increase of solution energies comparing with H m V complexes. In all the H m HeV complexes, the distances between any two H atoms are larger than that in a H 2 molecule, indicating that H 2 molecules can not be formed in these complexes. The trapping behaviours of He-vacancy complexes for H atoms are as follows: a HeV B e 1 and a HeV B e 3 complex can both trap up to three H atoms, a HeV B e 2 complex can capture up to two H atoms, and a HeV Ti complex can capture up to ten H atoms. The number of H atoms trapped by three types of HeV Be complexes reduces compared with that of mono-vacancy for H atoms, indicating that the retention of H atoms within the vacancy space in Be 12 Ti is suppressed by doping of He atom. The present results provide a foundational image of He-vacancy trapping mechanism for H atoms, which contributes significantly to the study on the synergistic effect of hydrogen and helium in tetragonal Be 12 Ti. [ABSTRACT FROM AUTHOR]

The state-of-the-art method generating potential functions used in molecular dynamics is based on machine learning with neural networks, which is critical for molecular dynamics simulation. This method provides an efficient way for fitting multi-variable nonlinear functions, attracting extensive attention in recent years. Generally, the quality of potentials fitted by neural networks is heavily affected by training datasets and the training process and could be ensured by comprehensively verificating the model accuracy. In this study, we obtained the neural network potential of face-centered cubic (FCC) Cu with the most accurate and adequate training datasets from first-principle calculations and the training process performed by Deep Potential Molecular Dynamics (DeePMD). This potential could not only succeed in reproductions of the variety of properties of Cu at 0 K, but also have a good performance at finite temperatures, such as predicting elastic constants and the melting point. Moreover, our potential has a better generalization capacity to predict the grain boundary energy without including extra datasets about grain boundary structures. These results support the applicability of the method under more practical conditions. [ABSTRACT FROM AUTHOR]

The effect of charged defects on the stability of implanted He and Y atoms has been fully investigated to gain insight into the occupation mechanism of defects in cubic ZrO2 using first-principles calculations. For the intrinsic point defects in ZrO2, the configurations of VO2+, IO2−, VZr4−, and IZr4+ are dominant, which have the lowest formation energy over the widest Fermi level range, respectively. He atoms at neutral Zr vacancies have the lowest incorporation energy (0.438 eV), illustrating that the VZr0 is probably the most stable trapping site for He atoms. For the Y atoms implanted in ZrO2, the most stable configuration of YZr1− is obtained over the widest Fermi level range. In the Y-doped ZrO2, the incorporation energy of He at the site of Oct2 interstitial is the lowest (1.058 eV). For He atoms trapped at vacancies, He-VZr0 has the lowest incorporation energy of 0.631 eV. These results indicate that He atoms preferentially occupy the sites of VZr0. The state of electric charge plays a significant role in the formation of defects in the ionic compound. The present simulation results provide a theoretical foundation for the effect of charged defects on the stability of He atoms, which contributes to the understanding of the microscopic solution behaviour of He atoms in perfect ZrO2 and Y-doped ZrO2. [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed to investigate the interaction between solute impurity O and H/He/vacancy irradiation defects in Ti3AlC2. The formation energy and occupation of O atoms within different defects as well as the trapping progress of O/H clusters are discussed. It is found that the O atom preferentially occupies the hexahedral interstitial site (Ihex-1) in bulk Ti3AlC2, whereas it prefers to occupy the neighbouring tetrahedral interstitial site (Itetr-2) within pre-exisiting Al monovacancy (VAl), Al divacancy (2VAl–Al) and the 2VAl–C divacancy composed of Al and C vacancies. The appearance of C vacancy could greatly reduce the oxygen formation energy and make an O atom more inclined to occupy the center of C vacancy. Vacancy could capture more O atoms than H/He atoms, where VAl and 2VAl–Al could hold up to fifteen and eighteen O atoms, respectively. Meanwhile, the O could also promote the formation of Al vacancy. On the other hand, O atoms tend to occupy the interstitial sites near the Al atomic layer and have attraction to Al atoms, which is likely to enable the O atoms to combine with the Al atoms to form a Al2O3 protective layer, thus effectively inhibiting further oxidation inside the Ti3AlC2. In addition, the H–O exhibits repulsion interaction, but strong attraction occurs in the He–O interaction. Therefore, the O atom has an inhibitory effect on the formation of the H cluster, while it could bind more He atoms to form a large number of He bubbles. Besides, the O impurity greatly reduces the trapping ability of vacancy to H atoms, and O and He have a synergistic interaction for inhibiting the aggregation of H clusters. The present results are expected to provide a new insight into the behaviour of Ti3AlC2 under irradiation and oxidation conditions so that structural materials could be better designed. [ABSTRACT FROM AUTHOR]

First-principles calculations have been conducted to investigate the interaction between vacancy defects and H/He impurity in Ti3AlC2. The formation energies of monovacancy and divacancy have been calculated. It is found that Al monovacancy (VAl), Al divacancy (2VAl–Al), and the divacancy composed of Al and C atoms (2VAl–C) are most easily formed in all vacancies. In addition, the interactions between multiple vacancies are weak. The formation of vacancy is relatively independent and not affected by other vacancies. The configurations and energies of H–mV (m = 0, 1, 2) complexes have been studied to assess the energetically favorable sites for H atoms. Within pre-existing VAl or 2VAl–Al, the most favorable site for H atoms is the Itetr-2 site, but the H atom tends to occupy the Ioct-4 site within 2VAl–C. The formation energies of the secondary vacancy defect nearest to an Al vacancy or C vacancy are significantly influenced by H impurity content. H clusters trapped in a primary Al vacancy can promote the formation of vacancy and prefer to form platelet-like bubbles parallel to the Al plane, while H clusters trapped in a primary C vacancy have higher probability to form spherical ones. The 2VAl–Al and 2VAl–C divacancies exhibit stronger H trapping ability than monovacancy. The 2VAl–Al divacancy could capture up to seven H atoms, and 2VAl–C could capture six H atoms. Meanwhile, the He–2VAl–Al complex could only capture four H atoms to form H–He hybridized bubbles, and He impurities effectively suppress further aggregation of H atoms. The present results provide microstructural images of nH–mV and nH–He–mV complexes as well as the evolution progress of H bubbles in Ti3AlC2, which is especially helpful for us to understand the behavior of H/He in Ti3AlC2 under irradiation. [ABSTRACT FROM AUTHOR]

The formation energies and formation volumes of the Ta, Al, and C vacancies in Ta2AlC have been calculated by using first-principles method. The results have shown that the vacancy formation is energetically most favorable for the C atom with formation energy of 1.72 eV. The formation energies of Ta and Al vacancies are 3.44 eV and 3.52 eV, respectively. The electronics properties show that the Ta vacancy has a clear effect on the conductivity of the Ta2AlC. This result indicates that Ta2AlC is a good candidate material for high-temperature and nuclear applications. [ABSTRACT FROM AUTHOR]