Manifestations of structural phase transition in ab initio molecular dynamics of (C3N2H5)2SbF5 crystal

Structural and electronic properties of the ferroelastic crystal (C3N2H5)2SbF5 characterized by first-order phase transition were studied by ab initio methods in the framework of density functional theory. The molecular dynamics calculations were performed at different temperatures in the range TC - 70 ÷ TC + 70° containing the phase transition point TC. In this approach, atomic scale (microscopic) manifestations of this transition were obtained. The quasi continuous temperature changes of some microscopic properties in the relatively wide temperature range around TC were observed in spite of sharp experimental temperature dependences of several macroscopic properties of (C3N2H5)2SbF5 near the first order phase transition point TC (latent heat flow, dielectric permittivity). The latter peculiarities may be regarded as the microscopic precursors of the first order phase transition in (C3N2H5)2SbF5. Different specific kinetic energies (energy per one atom) for five constituting chemical elements (C, N, H, Sb and F) of the crystal have been detected for the first time, indicating for different abilities of the interatomic energy exchange.