Shiba Hayato, Yamada Yasunori, Kawasaki Takeshi, Kim Kang
Institute for Solid State Physics, University of Tokyo, Chiba 277-8581, Japan.
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Phys Rev Lett. 2016 Dec 9;117(24):245701. doi: 10.1103/PhysRevLett.117.245701. Epub 2016 Dec 7.
By using large-scale molecular dynamics simulations, the dynamics of two-dimensional (2D) supercooled liquids turns out to be dependent on the system size, while the size dependence is not pronounced in three-dimensional (3D) systems. It is demonstrated that the strong system-size effect in 2D amorphous systems originates from the enhanced fluctuations at long wavelengths which are similar to those of 2D crystal phonons. This observation is further supported by the frequency dependence of the vibrational density of states, consisting of the Debye approximation in the low-wave-number limit. However, the system-size effect in the intermediate scattering function becomes negligible when the length scale is larger than the vibrational amplitude. This suggests that the finite-size effect in a 2D system is transient and also that the structural relaxation itself is not fundamentally different from that in a 3D system. In fact, the dynamic correlation lengths estimated from the bond-breakage function, which do not suffer from those enhanced fluctuations, are not size dependent in either 2D or 3D systems.
通过大规模分子动力学模拟发现，二维（2D）过冷液体的动力学依赖于系统尺寸，而在三维（3D）系统中尺寸依赖性并不明显。结果表明，二维非晶系统中的强系统尺寸效应源于长波长处增强的涨落，这与二维晶体声子的涨落类似。由低波数极限下的德拜近似组成的振动态密度的频率依赖性进一步支持了这一观察结果。然而，当长度尺度大于振动幅度时，中间散射函数中的系统尺寸效应可忽略不计。这表明二维系统中的有限尺寸效应是短暂的，并且结构弛豫本身与三维系统中的结构弛豫并无本质区别。事实上，由键断裂函数估计的动态关联长度在二维和三维系统中均与尺寸无关，因为它不受那些增强涨落的影响。
