Geometry and energetics of routes by which molecules are reoriented in a simple cubic phase of C*60

Alternative routes of interconversion of two orientational molecular states (double bond to pentagon and double bond to hexagon) coexisting in a simple cubic phase of C60 crystals are considered. A systematic computer-aided search based on the CRYCOM code package for comparing crystalline structures resulted in two types of solutions corresponding to a simple (congruent) and mirror routes of interconversion of spatial configurations. The second-type solutions - routes, two of which involved rotation of molecules through smaller angles (Ω=35° and 38.1°) than their earlier counterparts (Ω=41.8° and 60°), were previously unknown. The possibility of both types of interconversion routes is in line with the effect of merohedral twinning. The method of atom-atomic potentials invoked to calculate the optimum trajectories of transitions between the potential minima of the two states, passing through the appropriate stationary points, proved energetic unfavorableness of rotation of the molecules about the third-order axis compared to alternative routes. The mechanism of potential-barrier surmounting via relaxation of local nonequilibrium defect states formed by deceleration of independent rotations of the molecules is analyzed; the role of interfaces between domains in this mechanism is pointed out.