First Principles Simulation of Phosphorus-Selenium Systems

Car-Parrinello molecular dynamics simulations have been carried out for a single P4Se3 molecule and for an amorphous system of 72 atoms of overall stoichiometry P2Se. A systematic study have been made of the effects of variation in the basis set energy cut-off on the calculated bond lenghts and vibrational frequencies of the isolated molecule. We find that when a sufficiently large cut-off is used the calculated values are in good agreement with experiment. The simulation of the amorphous system was initiated from a configuration consisting of eight P4Se3 molecules and 16 added phosphorus atoms, prepared by a classical molecular dynamics calculation. After a total of approximately 10 ps Car-Parrinello simulation, only two molecules remained intact, but a varied of other partly ordered local structures were generated, including rings of phosphorus atoms and distorted versions of the P4Se3 molecule in which bonds between the basal phosphorus atoms had broken.