  Layered materials have huge potential in various applications due to their
extraordinary properties. To determine the interlayer interaction (or
equivalently the layer spacing under different perturbations) is of critical
importance. In this letter, we focus on one of the most prominent layered
materials, graphite, and theoretically quantify the relationship between its
interlayer spacing and the vibrational frequencies of its layer breathing and
shear modes, which are measures of the interlayer interaction. The method used
here to determine the interlayer interaction can be further applied to other
layered materials.
