The investigation of spatial correlations in liquid phosphorus by reverse monte-carlo calculations

The RMC method is used to model neutron diffraction results for liquid phosphorus. The adaptation of the basic routine for the treatment of molecular systems is described and the consequent changes in producing an initial configuration and achieving satisfactory convergence are critically examined. The programme is based on a structural unit of tetrahedral symmetry (P-4) and random moves involving both translation and rotation of the molecule are introduced and selected on the usual X(2) probability criteria. The resultant configuration is found to have a relatively simple centre-centre correlation function resembling that of an atomic liquid or a close-packed disordered array of spheres. The relative orientation of molecules within the first neighbour shell has been investigated and is found to differ from that proposed earlier from a simple consideration of geometrical anisotropy. The general use of RMC for molecular systems is discussed in relation to future work.