Uma entropia tetraédrica da água

A tetrahedral entropy for water

Pradeep Kumar a,1, Sergey V. Buldyrev b and H. Eugene Stanley c,1

- Author Affiliations

aCenter for Studies in Physics and Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021;

bDepartment of Physics, Yeshiva University, 500 West 185th Street, New York, NY 10033; and

cCenter for Polymer Studies and Department of Physics, Boston University, Boston, MA 02215

Contributed by H. Eugene Stanley, October 5, 2009 (received for review May 15, 2009)

Abstract

We introduce the space-dependent correlation function C Q(r) and time-dependent autocorrelation function C Q(t) of the local tetrahedral order parameter Q ≡ Q(r,t). By using computer simulations of 512 waterlike particles interacting through the transferable interaction potential with five points (TIP5 potential), we investigate C Q(r) in a broad region of the phase diagram. We find that at low temperatures C Q(t) exhibits a two-step time-dependent decay similar to the self-intermediate scattering function and that the corresponding correlation time τQ displays a dynamic cross-over from non-Arrhenius behavior for T > T W to Arrhenius behavior for T < T W, where T W denotes the Widom temperature where the correlation length has a maximum as T is decreased along a constant-pressure path. We define a tetrahedral entropy S Q associated with the local tetrahedral order of water molecules and find that it produces a major contribution to the specific heat maximum at the Widom line. Finally, we show that τQ can be extracted from S Q by using an analog of the Adam–Gibbs relation.

specific heat of water orientational entropy of tetrahedral liquids anomalies of liquid water Widom line

Footnotes

1To whom correspondence should be addressed. E-mail: pradeep.kumar@rockefeller.edu or hes@bu.edu

Author contributions: P.K., S.V.B., and H.E.S. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper.

The authors declare no conflict of interest.

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