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MD-Simulation of Viscous Toluene

MD-Simulation of Viscous Toluene. Ulf R. Pedersen & Thomas Schrøder. Department of Mathematics and Physics (IMFUFA), DNRF centre ”Glass and Time”, Roskilde University, Postbox 260, DK-4000 Roskilde, Denmark. Outline. Toluene like model. Molecular Dynamics are found using Newtonian mechanics.

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MD-Simulation of Viscous Toluene

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  1. MD-Simulation of Viscous Toluene Ulf R. Pedersen & Thomas Schrøder Department of Mathematics and Physics (IMFUFA),DNRF centre ”Glass and Time”,Roskilde University, Postbox 260,DK-4000 Roskilde, Denmark

  2. Outline

  3. Toluene like model • Molecular Dynamics are found using Newtonian mechanics. • Here, forces are given by Lennard-Jones potentials. Chemical structure of toluene A simple 1-component system that does not crystallize: Type A: OPLS-UA CH3 group Type B: Benzene from the Lewis-Wahnström OTP model 500 ns/day using 512 molecules on 4 processors The Lennard-Jones potential OPLS-UA: J. A. Chem Soc. 1984, vol. 106, p. 6638-6646 LW: Phys. Rev. E, 1994, vol, 50, num. 5, p. 3865-3877

  4. Structure g(r), radial distribution function A: methyl B: benzene ~0.40 nm ~0.55 nm ~0.73 nm

  5. The density during a cooling ramp Transition from liquid to solid on the simulated timescale Tm: Melting temperature Tc: Critical temperature where hopping accurse in dynamics Tg: Glass transition temperature (t = 100 s) Cooling rate: 37.5 K/ns

  6. Mean Square Displacement Diffusion constant 140K

  7. Van Hove correlation function at high temperature Hopping of methyl Hopping of benzene/CM ? 4pr2Gs(r,t) 4pr2Gs(r,t)

  8. Van Hove correlation function at low temperature Hopping of methyl Hopping of benzene/CM ? 4pr2Gs(r,t) 4pr2Gs(r,t)

  9. Two aspects of the dynamics, diffusion and rotation Non-exponential relaxation! Intermediate scattering function Dipole-dipole correlation Fit to stretch exponentals are shown, f(t)=A exp(-(t/t)g). t is a characteristic time, and g is the stretch

  10. Characteristic time and stretching exponents Non-Arrhenius relaxation! 140K (hopping) Characteristic times do not follow an Arrhenius law, t(T) = t0exp(Ea/kbT) Relaxation becomes more stretch with decreasing temperature

  11. Relaxation in time and frequency domain Prigogine-Defay ratio and the one-parameter hypothesis 130 K

  12. Conclution

  13. Future work • One-parameter hypothesis (Prigogine-Defay ratio) • Compare dynamics between idealized model and more realistic model • Finite size effects? notthe end …

  14. Mish The -process

  15. Movie Center of mass Methyl Quench dynamics at 120 K, 1 sek ~ 0.7 ns

  16. MSD and diffusion

  17. Mean Square Displacement 140K

  18. UA-OPLS 25 ns/day

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