Revised intermolecular potential with parameters depending on partial atomic charges for aromatic molecular systems

The practicablity and precision of the intermolecular potential was improved within the frame of an atom-atom approximation using 6-exp-1 type isotropic interatomic potentials without additional parameters. The improvement involves making the van der Waals parameters functions of the partial charges on constituent atoms supplement the classification of the parameter set, depending on atom type. The validity of the potential was confirmed with respect to crystal structures of polyacene (i.e., benzene, naphthalene, anthracene and tetracene) by molecular dynamics simulations.     

Solid structures of benzene at high pressures: molecular dynamics study

The structure of the experimentally-observed phase II of solid benzene at high pressures has been investigated through structural phase transitions in molecular dynamics simulations. Several structures are obtained by the pressure-induced phase transitions from the low-pressure phase I. Among them, the most possible structure is a high-pressure phase III with stacking faults, which is more stable than two structures previously proposed for the phase II by molecular packing analysis at high pressures. Furthermore, the experimental powder X-ray diffraction pattern for the phase II can be explained by the structure.     

Energy control of a molecular dynamics cell for the promotion of crystal phase transitions

A method for promoting crystal phase transitions in molecular dynamics (MD) simulations is proposed in which the temperature of a variable MD cell is controlled within the framework of the ParrinelleRahman constant-pressure method. This control is independent of the terqperature control of the molecules. The implementation makes it possible to perform MD simulations in which the temperature of the cell is high enough to enhance the deformation of the cell, while that of molecules is kept low so as not to lose the order of the crystal. The method successfully induced the phase transition of benzene crystals, which has not been obtained in MD simulations under usual conditions. Compared with the previously proposed method, i.e., momentum control of the cell, the present method is more favourable for reproducing experimentally observed structures.