Capillary waves

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(Thermal) capillary waves are oscillations of an interface which are thermal in origin (there are also capillary waves that are ordinary waves excited in an interface, such as ripples on a water surface.)

Capillary wave theory (CWT) is a classic account of how thermal fluctuations distort an interface (Ref. 1). It starts from some intrinsic surface that is distorted. A well-known prediction is that the width of the interface is bound to diverge with its area. However, this divergence is extremely weak, and is damped by the presence of an external field. For example, the action of gravity is sufficient to keep the width fluctuation on the order of one molecular diameter for areas of about 1 mm2 (Ref. 2).

Recently, a procedure has been proposed to obtain a molecular intrinsic surface from simulation data (Ref. 3). The density profiles obtained from this surface are, in general, quite different from the usual mean density profiles.


  1. F. P. Buff, R. A. Lovett, and F. H. Stillinger, Jr. "Interfacial density profile for fluids in the critical region" Physical Review Letters 15 pp. 621-623 (1965)
  2. J. S. Rowlinson and B. Widom "Molecular Theory of Capillarity". Dover 2002 (originally: Oxford University Press 1982)
  3. E. Chacón and P. Tarazona "Intrinsic profiles beyond the capillary wave theory: A Monte Carlo study", Physical Review Letters 91 166103 (2003)
  4. P. Tarazona, R. Checa, and E. Chacón "Critical Analysis of the Density Functional Theory Prediction of Enhanced Capillary Waves", Physical Review Letters 99 196101 (2007)