Molecular dynamics simulation of SnF$_2$ nanostructures in the internal channels of single-walled carbon nanotubes

A molecular dynamics simulation of solid tin(II) fluoride nanostructures formed in internal channels of single-walled carbon nanotubes (SWCNTs) has been performed using two types of model potentials–without and with inclusion of the polarization of ions. For the potential taking into account the polarization of ions, an ordered SnF$_2$2@SWCNT structure is reproduced: in SWCNT(10, 10), it has the form of the SnF$_2$ internal nanotube. At the same time, the SnF$_2$@SWCNT(11,11) structure is substantially disordered (glass-like). It has been found that heating of the SnF$_2$@SWCNT model system produces a superionic state characterized by a high mobility of fluorine ions without migration of tin ions. The model potentials disregard the covalent character of Sn–F bonds and the specific interactions of a lone electron pair of the Sn$^{2+}$ ion. This makes it impossible to completely reproduce the properties of SnF$_2$ at normal pressures. However, some characteristics of the SnF$_2$ high-pressure modification can be reproduced if the polarization of ions is taken into account.