The electronic properties of the coordination structure were analyzed by means of Bader partial charge using a code developed by the Henkelman group. The space distributions of electrons for all RE-O bonds were analyzed using line profiles of electron density ρ(x), as calculated from Gaussian-cube format data obtained from wave The formation mechanisms of these boron units were analyzed using transition matrices, which were defined as the unit changes either side of an AIMD step. Transitions between polymers with and without 3-rings were frequently observed in the melt; the reaction routes from polymer units with 3-rings to isolated units are less likely in the melt; this is associated with the stabilization of polymers by 3-ring formation.