Thermally Driven Capillary Fluctuations of Large Argon-like Clusters
D. I. Zhukhovitskii
Joint Institute of High Temperatures,
Russian Academy of Sciences,
Izhorskaya ul. 13, Bd. 2, Moscow, 125412 Russia
Abstract—Spectra of the cluster surface equilibrium fluctuations are treated by decomposition into the bulk and net capillary ones. The bulk fluctuations without capillary ones are simulated by the surface of a cluster truncated by a sphere. The bulk fluctuations spectrum is shown to be generated primarily by the discontinuity in spatial distribution of cluster internal particles. The net capillary fluctuations slice spectrum is obtained in molecular dynamics simulation by subtraction of the bulk fluctuations spectrum from the total one. This net spectrum is in the best agreement with a theoretical estimation if we assume the bare surface tension to be independent of the wave number. The wave number cutoff is brought in balance with the bare surface tension and excess surface area induced by the capillary fluctuations. It is shown that the ratio of the ordinary surface tension to bare one can be considered as a universal constant independent of the temperature and cluster size. Data obtained by molecular dynamics simulation are used to find the effective surface tension for the capillary fluctuations, which characterizes the deviation of Fourier spectrum obtained in simulation from the spectrum of macroscopic capillary waves. The variational method was used to recover this quantity from simulation data. It is revealed that the effective surface tension is almost constant within a rather wide wavelength range.