ABSTRACT
For instance, quantifying the time evolution of collective properties, such as the overall motion for one type of ions, or the overall shear stress in the system, provides access to transport coefficients and, in these two examples, conductivity and viscosity. The botanist Robert Brown initially observed the existence of constant and irregular motion in suspensions or fluids during the first part of the 19th century. Correlation functions are powerful tools for analyzing the behavior of molecular systems. Correlation functions can quantify spatial correlations, which are measures of the spatial interdependence between atoms and molecules, and provide microscopic insight into the structure of atomic and molecular systems. The time-correlation function measures how fluctuations at different times are correlated. Time-correlation functions provide a direct access to transport coefficients. The correspondence between time correlation functions and transport coefficients goes well beyond the example of diffusion.
