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Bangalore, June 2004. Potential Energy Landscape Description of Supercooled Liquids and Glasses. Why do we case ? Thermodynamics and Dynamics Review of thermodynamic formalism in the PEL approach Comparison with numerical simulations Development of an PEL EOS
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Bangalore, June 2004 Potential Energy Landscape Description of Supercooled Liquids and Glasses
Why do we case ? Thermodynamics and Dynamics Review of thermodynamic formalism in the PEL approach Comparison with numerical simulations Development of an PEL EOS Extention to non-equilibrium case (one or more fictive parameters ?) Outline
Why do we care ? Dynamics Why do we care: Dynamics A slowing down that cover more than 15 order of magnitudes P.G. Debenedetti, and F.H. Stillinger, Nature 410, 259 (2001).
Why do we care:Thermodynamics Why do we care Thermodyanmics A vanishing of the entropy difference at a finite T ?
Separation of time scales f(t) f(t) van Megen and S.M. Underwood Phys. Rev. Lett. 70, 2766 (1993) Glass Supercooled Liquid log(t)
Potential Energy Landscape, a 3N dimensional surface Statistical description of the number, depth and shape of the PEL basins e IS P IS w The PEL does not depend on TThe exploration of the PEL depends on T
fbasin i(T)= eIS+ kBTSln [hwj i/kBT] + fanharmonic i(T) fbasin i(T)= -kBT ln[Zi(T)] normal modes j Z(T)= S Zi(T) allbasins i
Thermodynamics in the IS formalism Stillinger-Weber F(T)=-kBT ln[W(<eIS>)]+fbasin(<eIS>,T) with Basin depth and shape fbasin(eIS,T)= eIS+fvib(eIS,T) and Number of explored basins Sconf(T)=kBln[W(<eIS>)]
Specific Heat Time-Dependent Specific Heat in the IS formalism
Distribution of local minima (eIS) Real Space Configuration Space + Vibrations (evib) rN evib eIS
<eIS>(T) (steepest descent minimization) fbasin(eIS,T) (harmonic and anharmonic contributions) F(T) (thermodynamic integration from ideal gas) From simulations….. F(T)=-kBT ln[W(<eIS>)]+fbasin(<eIS>,T) E. La Nave et al., Numerical Evaluation of the Statistical Properties of a Potential Energy Landscape, J. Phys.: Condens. Matter 15, S1085 (2003).
BKS Silica Eis nel tempo
Evaluete the DOS diagonalization
Harmonic Basin free energy Very often approximated with……
Vibrational Free Energy kBTSjln [hwj(eIS)/kBT] LW-OTP SPC/E S ln[wi(eIS)]=a+b eIS
f anharmonic anharmonic eIS independent anharmonicity Weak eIS dependent anharmonicity
Caso r2 per n-2n
The Random Energy Model for eIS Hypothesis: e-(eIS -E0)2/2s 2 W(eIS)deIS=eaN -----------------deIS 2ps2 S ln[wi(eIS)]=a+b eIS Predictions: <eIS(T)>=E0-bs 2 - s 2/kT Sconf(T)=aN-(<eIS (T)>-E0)2/2s 2
Gaussian Distribution ? eIS=SeiIS E0=<eNIS>=Ne1IS s2= s2N=N s21
T-dependence of <eIS> SPC/E LW-OTP T-1 dependence observed in the studied T-range Support for the Gaussian Approximation
BMLJ Sconf BMLJ Configurational Entropy
The V-dependence of a, s2, E0 e-(eIS -E0)2/2s 2 W(eIS)deIS=eaN -----------------deIS 2ps2
Landscape Equation of State P=-∂F/∂V|T F(V,T)=-TSconf(T,V)+<eIS(T,V)>+fvib(T,V) In Gaussian (and harmonic) approximation P(T,V)=Pconst(V)+PT(V) T + P1/T(V)/T Pconst(V)= - d/dV [E0-bs2] PT(V) =R d/dV [a-a-bE0+b2s2/2] P1/T(V) = d/dV [s2/2R]
SPC/E P(T,V)=Pconst(V)+PT(V) T + P1/T(V)/T FS, E. La Nave, and P. Tartaglia, PRL. 91, 155701 (2003)
Eis e S conf for silica… Esempio di forte
AG per Silica Correlating Thermodynamics and Dynamics: Adam-Gibbs Relation BKS Silica Ivan Saika-Voivod et al, Nature 412, 514 (2001).
V ~ (s/r)-n Soft Spheres with different softness
Conclusion I The V-dependence of the statistical properties of the PEL can be quantified for models of liquids Accurate EOS can be constructed from these information Interesting features of the liquid state (TMD line) can be correlated to features of the PEL statistical properties Connections between Dynamics and Thermodynamics
Aging in the PEL-IS framework Ti Tf Tf Starting Configuration (Ti) Short after the T-change (Ti->Tf) Long time
Evolution of eIS in aging (BMLJ) W. Kob et al Europhys. Letters 49, 590 (2000). One can hardly do better than equilibrium !!
Which T in aging ? F(T, Tf)=-TfSconf (eIS)+fbasin(eIS,T) Relation first derived by S. Franz and M. A. Virasoro, J. Phys. A 33 (2000) 891, in the context of disordered spin systems
Fluctuation Dissipation Relation (Cugliandolo, Kurcian, Peliti, ….) FS and Piero Tartaglia Extension of the Fluctuation-Dissipation theorem to the physical aging of a model glass-forming liquid Phys. Rev. Lett. 86, 107 (2001).
Soft sphere F(V, T, Tf)=-TfSconf (eIS)+fbasin(eIS,T) Support from the Soft Sphere Model
P(T,V)= Pconf(T,V)+ Pvib(T,V) From Equilibrium to OOE…. If we know which equilibrium basin the system is exploring… eIS, V, T .. We can correlate the state of the aging system with an equilibrium state and predict the pressure (OOE-EOS) eIS acts as a fictive T !
Numerical TestsLiquid-to-Liquid S. Mossa et al. EUR PHYS J B 30 351 (2002) T-jump at constant V P-jump at constant T