Tatsuya Yokoi

Artificial neural-network (ANN) interatomic potentials for simulating atomic structures and energetics of grain boundaries (GBs) in silicon were constructed and integrated into structural optimization and molecular dynamics (MD) algorithms. A training dataset including various atomic environments of symmetric tilt GBs was generated by performing density-functional-theory (DFT) calculations. The ANN potential after training was found to be capable of approximating the potential-energy surface at

The energetically favorable spatial configuration of M(3+) ions and oxide-ion vacancies near a symmetrical grain boundary (GB) in cubic zirconia is determined for various trivalent species M(3+) (M = Al, Sc, Y, Gd, La), and the driving force for grain boundary segregation (GBS) quantitatively examined using atomistic Monte Carlo simulations in conjunction with static lattice calculations. For a high concentration of ∼10 mol %, it is found that point defects near a GB plane preferentially occupy

To accurately predict grain boundary (GB) atomic structures and their energetics in CdTe, the present study constructs an artificial-neural-network (ANN) interatomic potential. To cover a wide range of atomic environments, large amounts of density functional theory (DFT) data are used as a training dataset including point defects, surfaces and GBs. Structural relaxation combined with the trained ANN potential is applied to symmetric tilt and twist GBs, many of which are not included in the train

An artificial neural network (ANN) potential for Al, trained with density-functional-theory (DFT) data, is constructed to accurately predict lattice vibrational properties and thermodynamics of grain boundaries (GBs) in Al. The ANN potential is demonstrated to accurately predict not only atomic structures and energetics of the GBs at 0 K but also partial phonon densities of states and vibrational entropies, even for GBs absent in the training data sets. In addition, their total potential energie

First-principles lattice dynamics calculations were performed to reveal an atomic-level origin of excess vibrational entropies at grain boundaries (GBs) in MgO. Fourteen symmetric tilt GBs with various structural units were systematically examined. The excess vibrational entropies were found to vary depending on the individual GBs, and as a result, the relative thermodynamic stability of the GBs studied changed with temperature. The excess GB volumes were less correlated with the excess vibratio

The site-selective occupation of point defects, Y3+ ions (Y′Zr) and O2− vacancies (V\ddot{O}), and their associations at a symmetric tilt grain boundary (GB) are studied to understand their competitive contribution to energetically favorable atomic arrangements by using atomistic simulations. It is found that at the GB there are the favorable sites for segregation of an isolated Y′Zr and V\ddot{O}. This indicates that the driving force for the site-selective segregation is present. Moreover, our

First-principles lattice dynamics is applied to symmetric tilt grain boundaries (GBs) in Al, Si and MgO, with the goal of revealing critical factors in determining excess vibrational entropies at the atomic level. Excess vibrational entropies at GBs are found to vary depending on the substances. Al GBs tend to show larger excess entropies and hence larger temperature dependence of the GB free energies than those in Si and MgO. Most of the Si GBs show small excess entropies. For Al and MgO, atom-