Calculation Of Soild-liquid Interfacial Free Energy By Molecular Dynamics Simulation

Both the magnitude and anisotropy of solid-liquid interfacial free energy arecrucial parameters in determining the kinetics and morphology of crystal nucleationand crystal growth. The energy barrier of crystal nucleation is determined by themagnitude of solid-liquid interfacial free energy. While dendrite shapes aredetermined by the anisotropy of solid-liquid interfacial free energy. Despite itsimportance, direct experimental measurements are difficult, as the solid-liquidinterfacial free energies are very small and the interface lies between two condensedphase.The development of computer science and computer method enable the study ofproperties of solid-liquid interface through computer simulation. Although theproperties of crystal-melt interfaces have been extensively studied in pure metals andsimple binary alloy, interfacial free energy and its anisotropy of succinonitrile remainrelatively poorly studied. Succinonitrile is a kind of special organic crystal which hassimilar interface roughness with metal. Many of the major progress of solidificationtheory take the experimental result of succinonitrile as basis to be recognized by theacademia, and is then conformed by the experimental result of other metals and alloy.Therefore, this paper aims to the problems with calculating solid-liquidinterfacial free energy by molecular dynamics simulation, develops critical nucleusmethod to calculate the anisotropy of solid-liquid interfacial free energy and comparewith the capillary fluctuation method. Then, the solid-liquid interfacial property ofsuccinonitrile is studied to complete the study of solid-liquid interfacial property ofmolecule crystal and establish the foundation data of solidification theory. The mainresearch findings are:1. The model of homogeneous nucleation is developed basing on growth andmelting behaviors of crystal nucleus in undercooled melt, and the critical temperatureof crystal nucleus with particular radius is determined. The relation between thecritical temperature and crystal nucleus radius is consistent with classical nucleationtheory, which is the foundation on calculating solid-liquid interfacial free energy bycritical nucleus method;2. Critical nucleus method is developed to calculate both the magnitude and anisotropy of solid-liquid interfacial free energy. The reliableness of critical nucleusmethod in calculating both the magnitude and anisotropy of solid-liquid interfacialfree energy is validated by comparing the results with the calculating results of thecapillary fluctuation method and experimental results.a) Solid-liquid interfacial free energies of8face center cubic metals arecalculated by critical nucleus method，the calculation results are consistent with theexperimental results, both the solid-liquid interfacial free energies and enthalpies ofmelting are linear with the melting points and the proportionality coefficients areconsistent with the experimental results within the error bar;b) The maximum undercoolings of8face center cubic metals are calculated bymolecular dynamics simulation. The maximum undercoolings are linear with themelting points. When the minimum crystal nucleus radius is three times its crystallattice constant, the proportionality coefficient between the maximum undercoolingsand the melting points is consistent with the experimental result within the error bar;c) Critical nucleus method is developed to calculate both the magnitude andanisotropy of solid-liquid interfacial free energy. The shape of crystal nucleus ischanged and certain crystal face is in touch with undercooled melt, solid-liquidinterfacial free energy of certain crystal face is then calculated;d) Both the magnitude and anisotropy of solid-liquid interfacial free energies ofCu and Ni are calculated by capillary fluctuation method, the calculation results areconsistent with the results of critical nucleus method within the error bar, therefore,the reliableness of critical nucleus method is validated;3. Solid-liquid interfacial free energy of succinonitrile is calculated by capillaryfluctuation method. The average solid-liquid interfacial free energy of succinonitrile is(8.37±0.84)mJ/m2, the anisotropy parameters1=0.011±0.009,2=0.0016±0.0012.The effect of system size on calculation result is also studied. The calculationprecision increases with the increase of system size.