First-principles simulation of phosphorus-selenium systems

Car-Parrinello molecular dynamics calculations have been carried out for a single P4Se3 molecule and for an amorphous system of 72 atoms of overall stoichiometry P2Se. A systematic study has been made of the effects of variation in the basis set energy cutoff on the calculated bond lengths and vibrational frequencies of the isolated molecule. We find that when a sufficiently large cutoff 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 variety of other partly ordered local structures were generated, including rings of phosphorus atoms and distorted versions of the P4Se3 molecule in which bonds between basal phosphorus atoms had broken.