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Rattling motion of fillers in cage materials has been of great interest for their import roles in superconductivity and thermoelectric applications. The standing waves of the rattling oscillations are normally lower in energy than the propagating waves of the acoustic phonons, thus exert large influences on the configuration of phonon dispersions as well as the associated thermal and electrical properties. Although it has been extensively studied, the origin of the low energy soft modes is still not clear. In the present paper, we show that van der Waals-type interactions are predominant between fillers and their surrounding cage frameworks, which explains the origin of the low energy modes in cage materials as a universal rule. Mass, free space and chemical environment of guest atoms are shown to be the most important factors to determine the three dimensional van der Waals-type interactions. The present work is mainly focused on type-I clathrates, skutterudites and pyrochlores.
The exfoliation of two naturally occurring van der Waals minerals, graphite and molybdenite, arouse an unprecedented level of interest by the scientific community and shaped a whole new field of research: 2D materials research. Several years later, t
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Three-dimensional epitaxial heterostructures are based on covalently-bonded interfaces, whereas those from 2-dimensional (2D) materials exhibit van der Waals interactions. Under the right conditions, however, material structures with mixed interfacia
The promise of high-density and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. At the same time, layered structures provide a new platform for
Large biomolecular systems, whose function may involve thousands of atoms, cannot easily be addressed with parameter-free density functional theory (DFT) calculations. Until recently a central problem was that such systems possess an inherent sparsen