Molecular Dynamics Simulations Of Crystal Growth Research Articles

Bayesian Data Assimilation of Temperature Dependence of Solid-Liquid Interfacial Properties of Nickel.

Temperature dependence of solid–liquid interfacial properties during crystal growth in nickel was investigated by ensemble Kalman filter (EnKF)-based data assimilation, in which the phase-field simulation was combined with atomic configurations of molecular dynamics (MD) simulation. Negative temperature dependence was found in the solid–liquid interfacial energy, the kinetic coefficient, and their anisotropy parameters from simultaneous estimation of four parameters. On the other hand, it is difficult to obtain a concrete value for the anisotropy parameter of solid–liquid interfacial energy since this factor is less influential for the MD simulation of crystal growth at high undercooling temperatures. The present study is significant in shedding light on the high potential of Bayesian data assimilation as a novel methodology of parameter estimation of practical materials an out of equilibrium condition.

MD simulation of crystal growth of NaCl from its supersaturated aqueous solution

Crystal growth from a supersaturated NaCl aqueous solution has been studied by molecular dynamics (MD) simulation. The model was similar to the one previously applied by us for a NaCl melt. 168Na +, 168Cl − and 192H 2O were set up in a basic cell in the following way: four layers of a NaCl seed crystal were disposed with the (100) plane of 32(Na ++Cl −) in contact with a supersaturated NaCl aqueous solution consisting of 40(Na ++Cl −) and 192H 2O. The solution was first equilibrated in contact with the ‘frozen’ crystal. Two-dimensional periodical conditions were imposed in the directions along the interface. In the direction normal to the interface, the aqueous solution is directly open to vacuum. Only one combination of pair potentials among the five different combinations of inter atomic potentials studied led to crystallization of NaCl. Thus, it strongly depends on the pair potentials used whether a crystal grows from its aqueous solution. After the equilibration run, a run longer than 2 ns was performed. Crystals gradually grew as clusters in the solution, but not uniformly on the seed crystal, which is in contrast to the growth from a NaCl melt.

MD simulation of crystal growth from CaCl 2 melt

Crystal growth from supercooled CaCl 2 melt has been studied by molecular dynamics (MD) simulation; the crystal has a distorted rutile type. The MD model was similar to that previously applied for NaCl. The Busing-type pair potentials the parameters of which were presented by Umesaki and Iwamoto were employed. The cases were studied that the initial interfaces between crystal and melt were the (001), (100) and (110) planes. The crystal grew only in the (001) case by MD of a nanosecond order, presumably because on every plane parallel to the (001) plane the charge neutrality is maintained. The maximum growth rate at about 100 K below the melting point was about 1 m/s, which is lower than that of NaCl-type structured crystals such as NaCl and MgO by about two orders of magnitude. The relatively slow rate may be due mainly to easy generation of the defects of this crystal which consists of ions with a ratio of one cation to two anions. The very small volume expansion on melting (0.5%) inherent in CaCl 2 seems not to play a special role on the growth rate.

Molecular-dynamics simulations of crystal growth from melted Si: Self-interstitial formation and migration

Molecular-dynamics simulations of crystal growth from melted Si have been performed using the Tersoff potential to analyze the defect formation and migration processes. We observed that a five-membered ring generated at the solid/liquid interface initiated self-interstitial defect formation. The formation and migration energies of the obtained defect were calculated to be 3.85 and 0.94 eV, respectively. The sum of the calculated formation and migration energies, 4.79 eV, is in good agreement with the experimental activation energy of self-diffusion in crystal Si.

MD simulation of crystal growth from MgO melt

By molecular dynamics (MD) simulation crystal growth from supercooled MgO melt has been studied, whose crystal has an NaCl type. The model was similar to that previously applied for NaCl. Crystal growth of the melt on the crystal layers has been studied; 1400 or 1800 ions were disposed in an MD basic cell. The Gilbert-Ida-type pair potentials whose parameters were presented by Kawamura and Akamatsu were employed, with which the melting point simulated in a three-dimensional space was 2670 K, while the experimental m.p. is 3099 K. The cases were studied that the initial interfaces between crystalline and melt were the (100), (110) and (111) planes; crystal grew in the [100], 〈100〉 and [111] directions, respectively. For the (100) system the growth rate was studied at various temperatures and found to possess a maximum(ca. 90 m s −1) at about 2300 K. The mean square displacements on the x−y plane and in the z-direction were calculated. The overall profile of the growth feature of MgO is very similar to that of NaCl.