The dynamics of a dense Pb wetting layer on the Si(111) surface is studied in the framework of a generalized Frenkel-Kontorova model. Instead of the typical diffusion by random hopping processes, a liquidlike collective motion of the Pb atoms within the dense wetting layer is revealed to give rise to ultrafast kinetics of the wetting layer even at low temperatures. A kinetic Monte Carlo simulation including this collective spreading mechanism of the dense wetting layer quantitatively reproduces the experimental observations.

Statistical contact potentials and bead-spring models have been widely used for computational studies of protein folding. However, there has been speculation that systematic error may arise in the contact energy calculations when the statistical potentials are deduced under the assumption that the chain connectivity in proteins can be ignored. To address this issue, we have performed molecular-dynamics simulations to study the structure and dynamics of a simple liquid system in which the beads are either connected or unconnected with springs. Results from the present study provide useful information for assessing the accuracy of the statistical potentials for protein structure simulations.