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Structural Order for One-Scale and Two-Scale Potentials

Structural Order for One-Scale and Two-Scale Potentials. Zhenyu Yan Advisor: H. Eugene Stanley Collaborators: Sergey V. Buldyrev, Nicolas Giovambattista,. Center for Polymer Studies and Department of Physics, Boston University For details see: Phys. Rev. Lett. 95, 130604 (Sep, 2005).

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Structural Order for One-Scale and Two-Scale Potentials

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  1. Structural Order for One-Scale and Two-Scale Potentials Zhenyu Yan Advisor: H. Eugene Stanley Collaborators: Sergey V. Buldyrev, NicolasGiovambattista, Center for Polymer Studies and Department of Physics, Boston University For details see: Phys. Rev. Lett. 95, 130604 (Sep, 2005)

  2. Motivation: anomalies of water Density anomaly of water Diffusion anomaly of water T=350k TMD T=220k DM DM: Diffusion Maximum/Minimum TMD: Temperature of Maximum Density Recent Finding in water: structural anomaly coupled with density and diffusion anomaly J. R.. Errington and P. G.Debenedetti,Nature409, 318 (2001).

  3. Questions ? 1. Arethe strong orientational tetrahedral interactions necessary for water anomalies ? 2. Can we find water-like anomalies in simple liquids (monatomic model with simple potential)? If YES, then what features should be present in the potential in order to get water-like anomalies ?

  4. The models: one-scale and two-scale ramp potentials one-scale two-scale U(r) U(r) σ0/ σ1=0 σ0 σ1 σ1 r r TMD, DM TMD, DM E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)

  5. Result: phase diagrams One-Scale Two-Scale isochores isochores DM TMD DM TMD Region of DM encloses the region of TMD

  6. What about the structural anomaly?

  7. How to quantify structural order Two basic types of order: . Orientational order: degree to adopt specific local structure (space angle) Water: tetrahedrality, Ramp potential: FCC Translational order t: degree to adopt preferential separations (distance) The value increases with increasing order

  8. Result: structural order for ramp potentials tmax tmin isotherms tmin tmax Qmax Qmax isotherms tmax and tmin for both one-scale and two-scale, Qmax only for two-scale ramp

  9. Result: order maps isotherm two-scale ramp water T=0.03 T=260k t t Q q water Q T=0.03 isotherms T=220k T=0.1 t T=260k Inaccessible region T=350k q Two-scale ramp order map is similar to water

  10. Result: anomalous regions of density, diffusion and structure water Qmax tmin tmax tmin Qmax DM tmax DM tmin DM TMD TMD TMD Two-scale ramp is similar to water

  11. Summary and Conclusion 1. Arethe strong orientational tetrahedral interactions necessary for water anomalies ? Not necessary 2. Can we find water-like anomalies in simple liquids with simple potentials ? yes If YES, then what features should be present in the potential in order to get water-like anomalies ? It suggests that the water-like behavior is related to two characteristic repulsive length scales in potentials.

  12. Thank you !

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