Structure factor and atomic dynamics of stable and supercooled liquid silicon by molecular dynamics (original) (raw)

Dynamic transitions in molecular dynamics simulations of supercooled silicon

Physical Review B, 2013

Two dynamic transitions or crossovers, one at a low temperature (T * ≈ 1006 K) and the other at a high temperature (T 0 ≈ 1384 K), are shown to emerge in supercooled liquid silicon using molecular dynamics simulations. The high-temperature transition (T 0 ) marks the decoupling of stress, density, and energy relaxation mechanisms. At the low-temperature transition (T * ), depending on the cooling rate, supercooled silicon can either undergo a high-density-liquid to low-density-liquid (HDL-LDL) phase transition or experience an HDL-HDL crossover. Dynamically heterogeneous domains that emerge with supercooling become prominent across the HDL-HDL transition at 1006 K, with well-separated mobile and immobile regions. Interestingly, across the HDL-LDL transition, the most mobile atoms form large prominent aggregates while the least mobile atoms get spatially dispersed akin to that in a crystalline state. The attendant partial return to spatial uniformity with the HDL-LDL phase transition indicates a dynamic mechanism for relieving the frustration in supercooled states.

Liquid–liquid phase transition in supercooled silicon

Nature Materials, 2003

S ilicon in its liquid and amorphous forms occupies a unique position among amorphous materials. Obviously important in its own right, the amorphous form is structurally close to the group of 4-4, 3-5 and 2-6 amorphous semiconductors that have been found to have interesting pressure-induced semiconductor-to-metal phase transitions 1,2 . On the other hand, its liquid form has much in common, thermodynamically, with water and other 'tetrahedral network' liquids that show density maxima 3-7 . Proper study of the 'liquid-amorphous transition', documented for non-crystalline silicon by both experimental and computer simulation studies 8-17 , may therefore also shed light on phase behaviour in these related materials. Here, we provide detailed and unambiguous simulation evidence that the transition in supercooled liquid silicon, in the Stillinger-Weber potential 18 , is thermodynamically of first order and indeed occurs between two liquid states, as originally predicted by Aptekar 10 . In addition we present evidence to support the relevance of spinodal divergences near such a transition, and the prediction 3 that the transition marks a change in the liquid dynamic character from that of a fragile liquid to that of a strong liquid.

Molecular dynamics simulation of the local inherent structure of liquid silicon at different temperatures

Physical Review B, 1999

Constant-volume and constant-temperature molecular dynamics simulations have been performed to study the inherent structural properties of liquid silicon (l-Si) at different temperatures by using Tersoff potential. Our results first show that the 50°-60°peak in bond angle distributions decomposes into two peaks, which are located 52°and 60°, and a new peak at 75°appears; the 52°peak disappears with a small cutoff distance. The bond length of bonds contributing to 52°peak is much greater than the cutoff distance of covalent bond. The height of 52°peak at first increases and then decreases with temperature, and has a maximum at a certain temperature. The probability of the covalent bonds whose bond angle is greater than 67°shows an anomalous decrease at a certain temperature. These anomalous features may play an important role on the anomalous behavior of some physical properties in l-Si such as electrical resistivity. The height of 60°and 75°peaks increases with temperature.

Nucleation of tetrahedral solids: A molecular dynamics study of supercooled liquid silicon

The Journal of Chemical Physics, 2009

The early stages of crystallization of tetrahedral systems remain largely unknown, due to experimental limitations in spatial and temporal resolutions. Computer simulations, when combined with advanced sampling techniques, can provide valuable details about nucleation at the atomistic level. Here we describe a computational approach that combines the forward flux sampling method with molecular dynamics, and we apply it to the study of nucleation in supercooled liquid silicon. We investigated different supercooling temperatures, namely, 0.79, 0.86, and 0.95 of the equilibrium melting point T m . Our results show the calculated nucleation rates decrease from 5.52Ϯ 1.75 ϫ 10 28 to 4.77Ϯ 3.26ϫ 10 11 m −3 s −1 at 0.79 and 0.86 T m , respectively. A comparison between simulation results and those of classical nucleation theory shows that the free energy of the liquid solid interface ␥ ls inferred from our computations differ by about 28% from that obtained for bulk liquid solid interfaces. However the computed values of ␥ ls appear to be rather insensitive to supercooling temperature variations. Our simulations also yield atomistic details of the nucleation process, including the atomic structure of critical nuclei and lifetime distributions of subcritical nuclei.

Polymorphism in glassy silicon: Inherited from liquid-liquid phase transition in supercooled liquid

Combining molecular dynamics (MD) simulation and Voronoi polyhedral analyses, we discussed the microstructure evolution in liquid and glassy silicon during cooling by focusing on the fraction of various clusters. Liquid-liquid phase transition (LLPT) is detected in supercooled liquid silicon However, freezing the high-density liquid (HDL) to the glassy state is not achieved as the quenching rate goes up to 10 14 K/s. The polyamorphism in glassy silicon is found to be mainly associated with low-density liquid (LDL).

In situ High-Energy X-Ray Diffraction Study of the Local Structure of Supercooled Liquid Si

Physical Review Letters, 2005

Employing the technique of electrostatic levitation, coupled with high-energy x-ray diffraction and rapid data acquisition methods, we have obtained high quality structural data more deeply into the supercooled regime of liquid silicon than has been possible before. No change in coordination number is observed in this temperature region, calling into question previous experimental claims of structural evidence for the existence of a liquid-liquid phase transition.