Capillary wave analysis of rough solid-liquid interfaces in nickel

Abstract

Crystal-liquid interfaces in nickel are investigated by molecular-dynamics computer simulations. Inhomogeneous systems of size Lx × Ly × Lz with Lz = 5Ly are prepared where the crystal fcc phase at different orientations coexists with the liquid phase, separated by planar interfaces in the xy-plane. The lateral dimensions are varied, using two different geometries with Lx = Ly and with Ly Lx. In the framework of capillary wave theory (CWT), anisotropic interfacial stiffnesses and tensions are determined using different predictions of CWT with respect to the spectrum, finite-size broadening and different geometries. From a parameterization in terms of cubic harmonics up to 8th order, the anisotropic interfacial free energy is obtained.

Bcc crystal-fluid interfacial free energy in Yukawa systems

“…In order to determine h( q), one has to employ a local criterion to distinguish between fluid and crystalline particles. Here, we follow our recent work 7,8 (110) orientation. Here, the Yukawa system 23 with a = 2.5 is considered.…”

“…7 First, the melting temperature T m is determined by analyzing the growth of inhomogeneous solidfluid systems at various undercoolings. Then, systems with solid-fluid interfaces at T m are prepared to analyze the longwavelength capillary wave fluctuations along the interface.…”

“…The melting temperature T m is estimated from the temperature dependence of the interface velocity as the point where the interface velocity is zero. 5,7 To prepare inhomogeneous systems, first, a bulk bcc crystal were placed into an elongated simulation box of size…”

“…The fluctuation of the local interface position is defined as h(x i , y i ) = z i − z i , where i denotes an atom on the surface and the brackets an instantaneous average over these atoms. In order to obtain h 2 ( q) , the points are mapped onto a regular grid on the xy plane using Shepard interpolation, 7 followed by the Fourier transformation of the interpolated heights. Figure 2 shows the q-dependent interfacial stiffnessγ (q) for the different orientations for the case a = 2.5 (note that the curves for a = 4.0 display a similar behavior and are therefore not shown here).…”

“…Recently, simulation schemes have been developed to access the interfacial free energy by studying the capillary wave fluctuations. [2][3][4][5][6][7][8] Even more challenging is a molecular theory predicting interfacial free energies. A necessary requirement to such theory is that it has to describe the crystal and the fluid phase in a unifying way.…”