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Monday, January 22, 2007
3:00 PM - 4:00 PM
CNLS Conference Room


Theory of Liquids and Landau’s “neither convincing nor useful” Epithet

Lawrence Pratt
LANL, T-12

We discuss broadly the molecular theory of liquids — as distinct from molecular simulation — which might respond to the challenge of Landau & Lifshitz:a

“We have not included in this book the various theories of ordinary liquids and of strong solutions, which to us appear neither convincing nor useful.”

We emphasize the importance of molecular liquids in the current research arenas of energy, the environment, biophysics, and nanotechnology. We discuss specifically liquid water: the most important liquid,b the condensed matter that fell on your head this morning, the matrix of life, and the central actor in NASA’s follow the water program for exploration of our solar system. The contrast of liquid water with van der Waals liquids provides a theme for identifying a general-purpose molecular theory of liquids in response to Landau’s challenge. A crucial step is acknowledgement of a source of data not available to Landau: the output stream of molecular simulation calculations. What is further required then is attention to basic statistical issues, conditioning and realizability, for statistical models. The result is a general-purpose molecular theory that is structurally noncommittal, and works satisfactorily even for liquid water. Ancestors of that general-purpose theory — quasi-chemical theories — were available to Landau. Finally, from the basis of this new theory we discuss the current research question why the Debye-H¨uckel theory — which was included in the textbook of Landau & Lifshitz — doesn’t provide a convincing basis for studying aqueous electrolyte solutions at interesting non-vanishing concentrations.

a. STATISTICAL PHYSICS, L. D. Landau and E. M. Lifshitz, Volume 5 of Course of Theoretical Physics, Translated by J.B. Sykes and M. J. Kearsley, Second Revised and Enlarged Edition (Addison-Wesley,1969)
b. For an example, see: “Desalination roadmap seeks technological solutions to increase the nation’s water supply,”

Host: Andrei Piryatinski