Vibrational dynamics of extreme 2×2 and 3×3 potassium iodide nanowires encapsulated in single-walled carbon nanotubes

We study the normal vibrations of $2\ifmmode\times\else\texttimes\fi{}2$ and $3\ifmmode\times\else\texttimes\fi{}3$ potassium iodide (KI) crystalline nanowires embedded in single-walled carbon nanotubes (SWCNTs) by density functional theory calculations, accompanied by Raman spectroscopy measurements on SCWNTs infiltrated with KI. The calculated stand-alone KI nanowires are found to be fully stable, while their vibrational energies are very close to the additional low-frequency Raman lines experimentally detected in the KI@SCWNT systems and ascribed to the encapsulated KI crystals. The difference between the relaxed and observed geometries of the KI nanowires evidences an electron transfer from these nanowires to the surrounding SWCNTs. Calculated radial and tangential vibrational frequencies of KI nanowires compared to those of supplementary discovered Raman lines suggest that the nanowire-SWCNT interaction is of a van der Waals origin and exclude the possibility of functionalization between the KI nanocrystals and the nanotube walls.