Presentation on theme: "Konstanz, 14-18 September 2002 Potential Energy Landscape Equation of State Emilia La Nave, Francesco Sciortino, Piero Tartaglia (Roma) Stefano Mossa (Boston/Paris)"— Presentation transcript:
Konstanz, September 2002 Potential Energy Landscape Equation of State Emilia La Nave, Francesco Sciortino, Piero Tartaglia (Roma) Stefano Mossa (Boston/Paris) 5th Liquid Matter Conference
Outline Brief introduction to the inherent-structure (IS) formalism (Stillinger&Weber) Statistical Properties of the Potential Energy Landscape (PEL). PEL Equation of State (PEL-EOS) Aging in the IS framework. Comparison with numerical simulation of aging systems.
IS P e Statistical description of the number [ (e IS )de IS ], depth [e IS ] and volume [log( )] of the PEL-basins Potential Energy Landscape
Thermodynamics in the IS formalism Stillinger-Weber F(T)=-k B T ln[ ( )]+f basin (,T) with f basin (e IS,T)= e IS +f vib (e IS,T) and S conf (T)=k B ln[ ( )] Basin depth and shape Number of explored basins
Real Space rNrN Distribution of local minima (e IS ) Vibrations (e vib ) + e IS e vib
F(T)=-k B T ln[ ( )]+f basin (,T) From simulations….. (T) (steepest descent minimization) f basin (e IS,T) (harmonic and anharmonic contributions) F(T) (thermodynamic integration from ideal gas) Data for two rigid-molecule models: LW-OTP, SPC/E-H 2 0 In this talk…..
Basin Free Energy ln[ i (e IS )]=a+b e IS SPC/E LW-OTP normal modes f basin (e IS,T)= e IS +k B T ln [h j (e IS )/k B T] +f anharmonic (T) normal modes
The Random Energy Model for e IS Hypothesis: Predictions : e IS )de IS = e N de IS e -(e IS -E 0 ) 2 /2 2 2222 ln[ i (e IS )]=a+b e IS =E 0 -b 2 - 2 /kT S conf (T)= N- ( -E 0 ) 2 /2 2 normal modes
T-dependence of SPC/E LW-OTP
(SPC/E) T-dependence of S conf (SPC/E)
The V-dependence of , 2, E 0 e IS )de IS =e N de IS e -(e IS -E 0 ) 2 /2 2 2222
Landscape Equation of State P=-∂F/∂V |T F(V,T)=-TS conf (T,V)+ +f vib (T,V) In Gaussian (and harmonic) approximation P(T,V)=P const (V)+P T (V) T + P 1/T (V)/T P const (V)= - d/dV [E 0 -b 2 ] P T (V) =R d/dV [ -a-bE 0 +b 2 2 /2] P 1/T (V) = d/dV [ 2 /2R]
Comparing the PEL-EOS with Simulation Results (LW-OTP)
SPC/E Water P(T,V)=P const (V)+P T (V) T + P 1/T (V)/T
Conclusion I The V-dependence of the statistical properties of the PEL has been quantified for two models of molecular 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
Aging in the PEL-IS framework Starting Configuration (T i ) Short after the T-change (T i ->T f ) Long time TiTi TfTf TfTf
From Equilibrium to OOE…. P(T,V)= P conf (T,V)+ P vib (T,V) If we know which equilibrium basin the system is exploring… e IS acts as a fictive T ! e IS (V,T f ),V P conf e IS (V,T f ),V,T log( ) P vib
Numerical Tests Heating a glass at constant P T P time
Liquid-to-Liquid T-jump at constant V P-jump at constant T
Conclusion II The hypothesis that the system samples in aging the same basins explored in equilibrium allows to develop an EOS for OOE-liquids which depends on one additional parameter Short aging times, small perturbations are consistent with such hypothesis. Work is requested to evaluate the limit of validity. The parameter can be chosen as fictive T, fictive P or depth of the explored basin e IS
Perspectives An improved description of the statistical properties of the potential energy surface. Role of the statistical properties of the PEL in liquid phenomena A deeper understanding of the concept of P conf and of EOS of a glass. An estimate of the limit of validity of the assumption that a glass is a frozen liquid (number of parameters) Connections between PEL properties and Dynamics
References and Acknowledgements We acknowledge important discussions, comments, criticisms from P. Debenedetti, S. Sastry, R. Speedy, A. Angell, T. Keyes, G. Ruocco and collaborators Francesco Sciortino and Piero Tartaglia Extension of the Fluctuation-Dissipation theorem to the physical aging of a model glass-forming liquid Phys. Rev. Lett (2001). Emilia La Nave, Stefano Mossa and Francesco Sciortino Potential Energy Landscape Equation of State Phys. Rev. Lett., 88, (2002). Stefano Mossa, Emilia La Nave, Francesco Sciortino and Piero Tartaglia, Aging and Energy Landscape: Application to Liquids and Glasses., cond-mat/
Entering the supercooled region
Same basins in Equilibrium and Aging ?
f basin i (T)= -k B T ln[Z i (T)] all basins i f basin (e IS,T)= e IS + k B T ln [h j (e IS )/k B T] + f anharmonic (T) normal modes j Z(T)= Z i (T)
e IS = e i IS E 0 = =N e 1 IS 2 = 2 N =N 2 1 Gaussian Distribution ?
T-dependence of (LW-OTP)
Reconstructing P(T,V) P=-∂F/∂V F(V,T)=-TS conf (T,V)+ +f vib (T,V) P(T,V)= P conf (T,V) + P vib (T,V)
Numerical Tests Compressing at constant T PfPf T time PiPi