X-ray photon correlation spectroscopy (XPCS) allows for the resolution of dynamic processes within a material across a wide range of length and time scales. X-ray speckle visibility spectroscopy (XSVS) is a related method that uses a single diffraction pattern to probe ultrafast dynamics. Interpretation of the XPCS and XSVS data in terms of underlying physical processes is necessary to establish the connection between the macroscopic responses and the microstructural dynamics. To aid the interpretation of the XPCS and XSVS data, we present a computational framework to model these experiments by computing the X-ray scattering intensity directly from the atomic positions obtained from molecular dynamics (MD) simulations. We compare the efficiency and accuracy of two alternative computational methods: the direct method computing the intensity at each diffraction vector separately, and a method based on fast Fourier transform that computes the intensities at all diffraction vectors at once. The computed X-ray speckle patterns capture the density fluctuations over a range of length and time scales and are shown to reproduce the known properties and relations of experimental XPCS and XSVS for liquids.
翻译:X光X射线光相关光谱分析(XPCS)使动态过程能够在跨长和时间尺度的多种材料中解析。X射线分光分光光谱(XSVS)是一种相关方法,使用单一的分解模式探测超快动态。必须解释XPCS和XSVS数据的基本物理过程,以建立宏观响应和微结构动态之间的联系。为了帮助解释XPCS和XSVS数据,我们提出了一个计算框架,通过直接从分子动态模拟(MD)获得的原子位置计算X射线散布强度来模拟这些实验。我们比较了两种替代计算方法的效率和准确性:直接方法,分别计算每个分解矢量的强度,以及基于快速四倍变的方法,即一次性对所有折射矢量矢量的强度进行计算。计算X射线分光模式在长度和时间尺度范围内收集密度波动,用于复制已知XS和XS的实验特性和关系。