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Towards an atomistic description of the material response of glasses across all time-scales with Non-Affine Lattice Dynamics (NALD)

Date: 01.10.2018
Time: 10:00 a.m.
Place: ICAMS seminar room IC 02/718

Alessio Zaccone, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK

The material response of glasses is a topic of fundamental relevance in condensed matter physics, and also has plenty of applications in materials science and engineering. At present there is no theory which can describe the response of glasses below the glass transition temperature. We recently developed a new approach, called Non-affine Lattice Dynamics (NALD), to the linear response of glasses from first principles. Starting from a particle-bath Hamiltonian we derive a Generalized Langevin equation of motion for nonaffine atomic displacements under an external field [1-3]. This leads directly to expressions for the complex moduli (for e.g. viscoelastic or dielectric response) which involve the vibrational density of states (DOS) of the glass, together with a memory kernel for the friction. NALD has been shown to provide parameter-free predictions of viscoelastic moduli of polymer glasses in excellent agreement with numerical simulations at temperatures below and even slightly above Tg, provided that non-propagating instantaneous normal modes (INMs) are included in the DOS, which allows us to account for anharmonic effects [2]. NALD is currently being developed into atomic-scale calculations of real materials with the aim of providing parameter-free predictions of mechanical response across all time-scales/frequencies, thus solving the problem of ab-initio and atomistic approaches which are valid only at extremely high deformation rates/frequencies. Finally I will briefly review recent results about nonlinear response of metallic glasses [4], the origin of shear banding from alignment of Eshelby-like quadrupoles in metallic glasses [5] and a new theory of crystal nucleation in shear flows [6].

References:
[1] B. Cui, R. Milkus, and A. Zaccone. Direct link between boson-peak modes and dielectric alpha-relaxation in glasses. Physical Review E 95, 022603 (2017).
[2] B Cui, J. Yang, J. Qiao, M. Jiang, L. Dai, Y.-J. Wang, A. Zaccone. Atomic theory of viscoelastic response and memory effects in metallic glasses. Physical Review B 96, 094203 (2017).
[3] V.V. Palyulin, C. Ness, R. Milkus, R. M. Elder, T.W. Sirk, A. Zaccone. Parameter-free predictions of the viscoelastic response of glassy polymers from non-affine lattice dynamics. Soft Matter, DOI: 10.1039/c8sm01468j.
[4] A. Zaccone, P. Schall, E.M. Terentjev. Microscopic origin of nonlinear nonaffine deformation in bulk metallic glasses. Phys. Rev. B 90, 140203(R) (2014).
[5] V. Hieronymus-Schmidt, H. Roesner, G. Wilde, A. Zaccone. Shear banding in metallic glasses described by alignments of Eshelby quadrupoles. Phys. Rev. B 95, 134111 (2017).
[6] F. Mura and A. Zaccone. Effects of shear flow on phase nucleation and crystallization. Phys. Rev. E 93, 042803 (2016).

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