Computer simulations of heterogeneous crystal growth of atomic systems (original) (raw)
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Molecular dynamics methodology to investigate steady-state heterogeneous crystal growth
Chemical Physics, 2007
In this paper a new molecular dynamics simulation methodology to investigate steady-state heterogeneous crystal growth from a supercooled liquid is presented. The method is tested on pure component systems such as Lennard-Jonesium and water/ice, as well as multicomponent systems such as methane hydrate crystals. The setup uses periodicity in all three directions and two interfaces; at one interface, crystallization occurs, while at the other, melting is enforced by locally heating the crystal only near that interface. Steady-state conditions are achieved when the crystal is melted at the same rate as the growth occurs. A self-adaptive scheme that automatically modifies the rate of melting to match the rate of growth, crucial for establishing steady-state conditions, is described. In contrast with the recently developed method of Razul et al. ͓Mol. Phys. 103, 1929 ͑2005͔͒, where the rates of growth ͑melting͒ were constant and the temperatures determined, the present approach fixes the supercooling temperature at the growing interface and identifies the corresponding steady-state crystal growth rate that corresponds to the thermodynamic force provided. The static properties of the interface ͑e.g., the interfacial widths͒ and the kinetics of the crystal growth are found to reproduce well previous findings. The importance of establishing steady-state conditions in such investigations is also briefly discussed.
Molecular dynamics simulation of binary hard sphere crystal/melt interfaces
Molecular Physics, 1999
We examine, using molecular dynamics simulation, the structure and thermodynamics of the and (111) disordered face-centered cubic (FCC) crystal/melt interfaces for a binary hard-sphere system. This study is an extension of our previous work, [Phys. Rev. E 54, R5905 (1996)], in which preliminary data for the (100) interface were reported. Density and diffusion profiles on both fine-and course-grained scales are calculated and analyzed leading to the conclusion that equilibrium interfacial segregation is minimal in this system.
Towards an atomic-scale understanding of crystal growth in solution
Faraday Discussions, 2007
Our understanding of crystal growth continues to increase thanks to progress in theoretical models, computer simulations and experimental techniques. A discussion of the state-of-the-art in morphology prediction and of the determination of the solid-liquid interface structure using X-ray diffraction shows, however, that there is still a large gap between experiment and theory. We expect that computer modelling, in the form of both Molecular Dynamics simulations and first-principle calculations, will play a crucial role in filling this gap.
Journal of Computational Physics, 2005
A phase-field model for non-isothermal solidification in multicomponent systems [SIAM J. Appl. Math. 64 (3) (2004) 775-799] consistent with the formalism of classic irreversible thermodynamics is used for numerical simulations of crystal growth in a pure material. The relation of this approach to the phase-field model by Bragard et al. [Interface Science 10 (2-3) (2002) 121-136] is discussed. 2D and 3D simulations of dendritic structures are compared with the analytical predictions of the Brener theory [
Kinetics of rapid crystal growth: phase field theory versus atomistic simulations
IOP Conference Series: Materials Science and Engineering, 2019
Kinetics of crystal growth in undercooled melts is analyzed by methods of theoretical modeling. Special attention is paid to rapid growth regimes occurring at deep undercoolings at which non-linearity in crystal velocity appears. A traveling wave solution of the phase field model (PFM) derived from the fast transitions theory is used for a quantitative description of the crystal growth kinetics. The “velocity – undercooling” relationship predicted by the traveling wave solution is compared with the data of molecular dynamics simulation (MDS) which were obtained for the crystal-liquid interfaces growing in the 〈 100〉-direction in the Ni50Al50 alloy melt.
Molecular Dynamic Simulation of Directional Crystal Growth
Springer Proceedings in Physics, 2000
We use molecular dynamic to simulate the directional growth of binary mixtures. our results compare very well with analitical and experimental results. This opens up the possibility to probe growth situations which are difficult to reach experimentally, being an important tool for further experimental and theoretical developments in the area of crystal growth.
Particle-Based Computer Simulation of Crystal Nucleation and Growth Kinetics in Undercooled Melts
HERLACH:UNDERCOOLED MELTS O-BK, 2012
ABSTRACT Crystallization from the melt in Ni and Al50Ni50 is investigated using Monte Carlo (MC) as well as Molecular Dynamics (MD) simulation techniques. Crystal-liquid interfaces in Ni are analyzed in the framework of capillary wave theory (CWT). Anisotropic interfacial stiffnesses and tensions are determined by means of different predictions of CWT with respect to the spectrum, finite-size broadening and different geometries. Free energy barriers G for homogeneous nucleation in Ni are obtained from MC simulations in conjunction with umbrella sampling. These simulations indicate a non-spherical geometry of crystalline clusters, fluctuating between prolate and oblate shape at a given size. Nevertheless, the temperature dependence of G is well described by classical nucleation theory. Finally, the movement of planar solid-liquid interfaces in undercooled Ni is compared to that in the system Al50Ni50. In the latter binary system crystal growth is a factor of about 24 slower than in the one-component metal Ni. We show that this difference is associated with an additional segregation process in the binary system that occurs prior to the formation of a new crystalline layer.
Phase-Field Simulations of Crystal Growth
2010
This course gives an elementary introduction to the phase-field method and to its applications for the modeling of crystal growth. Two different interpretations of the phase-field variable are given and discussed. It can be seen as a physical order parameter that characterizes a phase transition, or as a smoothed indicator function that tracks domain boundaries. Elementary phase-field models for solidification and epitaxial growth are presented and are applied to the dendritic growth of a pure substance and the step-flow growth on a vicinal surface.
Molecular dynamics simulations of crystallization under confinement at triple point conditions
The Journal of Chemical Physics, 2003
Molecular dynamics computer simulations of crystallization of a Lennard-Jones system under confinement conditions in the vicinity of the triple point are reported. We calculate the force exerted on a crystal by a melt when it crystallizes. The force due to crystallization is reflected in the disjoining pressure isotherms as a characteristic peak. We find that at conditions of high confinement, i.e., pore thicknesses of ≈1 nm, the disjoining pressure can rise up to ≈108 Pa. We also analyze the dependence of the crystallization under confinement as a function of temperature. Confinement can stabilize the crystal phase at temperatures significantly higher than the melting temperature. For the systems studied in this work, a pore of 1 nm thickness stabilizes the crystal phase at temperatures up to 45% higher than the normal melting temperature. In addition we consider the disjoining pressure profile along confining pore slits of finite lengths. The finite size effects due to the pore le...
Modern nanoparticle research in the field of small metallic systems has con¯rmed that many nanoparticles take on some Platonic and Archimedean solids related shapes. A Platonic solid looks the same from any vertex, and intuitively they appear as good candidates for atomic equilibrium shapes. A very clear example is the icosahedral (Ih) particle that only shows f111g facets that contribute to produce a more rounded structure. Indeed, many studies report the Ih as the most stable particle at the size range r < 20 ºA for noble gases and for some metals. In this review, we report on the structure and shape of mono- and bimetallic nanoparticles in the wide size range from 1--300 nm. First, we present AuPd nanoparticles in the 1--2 nm size range that show dodecahedral atomic growth packing, one of the Platonic solid shapes that have not been identified before in this small size range for metallic particles. Next, with particles in the size range of 2--5 nm, we present an energetic surface reconstruction phenomenon observed also on bimetallic nanoparticle systems of AuPd and AuCu, similar to a re-solidification effect observed during cooling process in lead clusters. These binary alloy nanoparticles show the fivefold edges truncated, resulting in f100g facets on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence in the literature before. Next nanostructure we review is a monometallic system in the size range of ¼ 5 nm that we termed the decmon. We present here some detailed geometrical analysis and experimental evidence that supports our models. Finally, in the size range of 100--300 nm, we present icosahedrally derived star gold nanocrystals which resembles the great stellated dodechaedron, which is a Kepler-Poisont solid. We conclude then that the shape or morphology of some mono- and bimetallic particles evolves with size following the sequence from atoms to the Platonic solids, and with a slightly greater particle's size, they tend to adopt Archimedean related shapes. If the particle's size is still greater, they tend to adopt shapes beyond the Archimedean (Kepler-Poisont) solids, reaching at the very end the bulk structure of solids. We demonstrate both experimentally and by means of computational simulations for each case that this structural atomic growth sequence is followed in such mono- and bimetallic nanoparticles.