Structural Order for One-Scale and Structural Order for One-Scale and Two-Scale PotentialsTwo-Scale Potentials
Zhenyu YanZhenyu Yan
Advisor: Advisor: H. Eugene StanleyH. Eugene Stanley
Collaborators:Collaborators:Sergey V. Buldyrev, Sergey V. Buldyrev,
NicolasNicolas Giovambattista, Giovambattista,
Center for Polymer Studies and Department of Physics, Boston University
For details see: Phys. Rev. Lett. 95, 130604 (Sep, 2005)
Motivation: aMotivation: anomalies nomalies of waterof water
TMD
DM
TMD: Temperature of Maximum Density
Density anomaly of waterDensity anomaly of water Diffusion anomaly of waterDiffusion anomaly of water
DM: Diffusion Maximum/Minimum
Recent Finding in water: structural anomaly coupled with density and diffusion anomaly
J. R.. Errington and P. G. Debenedetti, Nature 409, 318 (2001).
T=350k
T=220k
Questions ?Questions ?
1. Are the 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 ?
The models: one-scale and two-scale The models: one-scale and two-scale ramp potentialsramp potentials
σ0/ σ1=0
r
U(r)
σ1 r
U(r)
σ1σ0
one-scale two-scale
TMD, DM TMD, DM
E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)
Result: phase diagramsResult: phase diagrams
isochores isochores
DMTMD
TMDDM
One-Scale Two-Scale
Region of DM encloses the region of TMD
What about the structural anomaly?What about the structural anomaly?
How to quantify structural orderHow to quantify structural order
Ramp potential: FCC
Two basic types of order:
. Orientational order: degree to adopt specific local structure (space angle)
Translational order t: degree to adopt preferential separationsseparations (distance)
Water: tetrahedrality,tetrahedrality,
The value increases with increasing order
drrgtcr
0
1)(
Result: structural order for ramp potentialsResult: structural order for ramp potentials
isotherms
tmax
tmin
Qmax
isotherms tmin
Qmax
tmax
tmax and tmin for both one-scale and two-scale, Qmax only for two-scale ramp
Result: order mapsResult: order maps
Two-scale ramp order map is similar to water
T=260k
isotherms
water
T=350k
T=220k
T=0.03
two-scale ramp
water
Inaccessible region
Q
t
isotherm
Q
t
q
q
t
T=260k
T=0.03
T=0.1
Result: anomalous regions of density, Result: anomalous regions of density, diffusion and structurediffusion and structure
tmax tmin
tmax tmin Qmax
water
Two-scale ramp is similar to water
TMD
DM
Qmax tmin
TMD
DM
TMD
DM
Summary and ConclusionSummary and Conclusion
1. Are the strong orientational tetrahedral interactions necessary for water anomalies ?
Not necessaryNot 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 It suggests that the water-like behavior is related to two characteristic repulsive length scales related to two characteristic repulsive length scales in potentials.in potentials.
Thank you !Thank you !