A successful example of visualization of quantitative structure-property relationship, relation between the anomalous distribution/dynamics of the guest atom “rattling” and the reduction of thermal conductivity in type-I clathrates, is introduced. We found that the area governed by the weakly bounded guest atom in the cage can be extracted using trace of electrostaticpotential local-minimum (EPLM). The area normalized by the size of guest atom, rattling factor, corresponds to degree of rattling, and thermal conductivity decreases with an increase of the rattling factor. The electrostatic potential distribution analysis will be a powerful tool to visualize quantitative structure-property relationship in many kinds of materials in which the novel properties originate from polarization, uneven distribution of electrons etc.
