Langevin-equation simulation is used to study the dynamics of a simple model of homopolymer collapse at infinite dilution for polymers of lengths N=100, 200, 300, 500, and 1024 units. Lennard-Jones potentials are chosen to represent the bead–bead interactions and a harmonic potential bonds nearest-neighbor beads. The Flory coil-to-collapsed globule transition is brought about by an adjustment of the Lennard-Jones potential interactions. The average cluster size and distribution, along with the radius of gyration are used to characterize the collapse dynamics. Our results indicate that there are several kinetic mechanisms that lead to a collapsed polymer. At early times the dominant mechanisms involve cluster creation and growth by adsorption of slack polymer, whereas for later times the mechanism involves cluster coarsening. For this latter mechanism we find that the average cluster size 〈s〉 grows as 〈s〉=Atz, where z is dependent on u3, the third virial coefficient. Depending on the value of u3 we determine two values for z, first, z=0.60±0.02 for u3 not equal to zero and second z=0.66±0.03 for u3 equal to zero, both representing a departure from Lifshitz–Slyozov theory.

This paper describes the techniques and methodologies employed during parallelization of the semi-empirical quantum-mechanical (SEQM) code MNDO, with the specific requirement that the program run efficiently on a range of distributed memory parallel platforms. We present two approaches which reflect the different ways in which this type of code are used. The central problem for one of these concerns the parallelization of a series of matrix operations of the type common to many computational applications (matrix-matrix multiplication and matrix diagonalisation). In particular, we provide one possible parallel solution which tackles the core double matrix multiplication. We discuss the preliminary results of our prototype port and indicate to what extent the parallel code can fulfill the requirements of industrial users