Modeling and first-principles calculation of low-frequency quasi-localized vibrations of soft and rigid As–S nanoclusters

Structural Nature of Boson Peak and Low‐Temperature Heat Excess in As2S3 Glass

“…The first two components of this band at 310 and 340 cm −1 are characteristic modes of symmetric and asymmetric As–S stretching vibrations of network‐forming AsS 3 pyramids, respectively, whereas the third component, located at about 390 cm −1 , is related to a “water‐like” –As–S–As– vibration. [ 1,45 ] Also, a small contribution from –S–S– bridging vibrations (having characteristic band at 492 cm −1 ) can be detected in the Raman spectrum of stoichiometric glass. The evidences of small concentration of homopolar As–As bonds in the structure of g‐As 2 S 3 can be found in the 100–250 cm −1 spectral region.…”

“…The local structure of noncrystalline As–S materials consisted of at least three types of topologies namely ring‐, branchy‐, and cage‐like ones. [ 44 ] First two represents structurally flexible nanocluster models, whereas the third type of nanoclusters (e.g., As 4 S 4 , As 4 S 3 , and so on) can be classified as structurally rigid model. In contrast with structurally rigid molecules which can rotate and vibrate, the structure of flexible (nonrigid) molecules was different allowing them to tunnel through a potential barrier from one configuration to another (conformational isomerism).…”

“…Further evaluation of calculated low frequency vibrations of branchy‐like As–S nanoclusters revealed that these vibrations were very sensitive not only to structural flexibility but furthermore also to the rigidity of the cluster edges which can be related to the level of connectivity of the clusters incorporated in the structural network. [ 45 ]…”