Long‐Range Forces in Rock‐Salt‐Type Tellurides and How they Mirror the Underlying Chemical Bonding

Chemical bonding in main‐group IV chalcogenides is an intensely discussed topic, easily understandable because of their remarkable physical properties that predestine these solid‐state materials for their widespread use in, for instance, thermoelectrics and phase‐change memory applications. The atomistic origin of their unusual property portfolio remains somewhat unclear, however, even though different and sometimes conflicting chemical‐bonding concepts have been introduced in the recent years. Here, it is proposed that projecting phononic force‐constant tensors for pairs of atoms along differing directions and ranges provide a suitable and quantitative descriptor of the bonding nature for these materials. In combination with orbital‐based quantitative measures of covalency such as crystal orbital Hamilton populations (COHP), it is concluded that the well‐established many‐center and even n‐center bonding is an appropriate picture of the underlying quantum‐chemical bonding mechanism, supporting the recent proposal of hyperbonded phase‐change materials. Examining the chemical bonding in rock‐salt‐type IV–VI functional materials by projected force constants as derived from ab initio thermochemistry yields unusually strong long‐range forces along the cubic lattice vectors, impossible to account for by either two‐center covalent or ionic bonding. The full analysis, including orbital‐based bonding descriptors, points toward hyperbonding, thereby explaining certain unique properties of this material class.