International Workshop on Challenges of Atomistic Simulations of Glasses and Amorphous Materials

In contrast to diffraction methods, which deal with the coherence lengths ofabout 150 –200 nm, only very few unit cells of a definite structure are required forRaman scattering identification. This allows the micro-structural analysis ofamorphous materials. However, until the vibrational properties of glasses are betterunderstood in terms of their structure and bonding, vibrational spectroscopy can notbe rigorously used as a tool for probing their detailed molecular structure. In thisreport, based on the ab-initio calculations of normal Raman mode, combined withgroup theory analysis, we revealed the subtle evolution of local nearest neighborconnectivity of structural units in glasses, indicating the high sensitivity of Ramanscattering to structural change in glasses. Keyword: glasses, structure, ab initio calculations Acknolwlegement: NSFC(Nos.51172169,51372180), NCET(NCET-11-0687), NSF ofHubei Province(No.2013CFA008), and the key technology innovation project ofHubei Province (Nos.2013AEA005). Molecular Modeling of Gas Adsorption in Bulk and Porous SilicaB. Coasne1 Multiscale Material Science for Energy and Environment 2, UMI 3466 CNRS-MIT, 77Massachusetts Avenue, Cambridge MA, 2 Department of Civil Environmental Engineering,Massachusetts Institute of Technology, MA, USA Adsorption in amorphous porous solids such as silica glasses is at the heart of importantapplications: catalysis, energy, environment, etc. From a computational point of view,understanding the adsorption and transport of fluids in such complex amorphous materials requiresdeveloping realistic models. In this work, I will show how a multiscale strategy, using both firstprinciples and classical atomistic simulations, can be used to develop and investigate the propertiesof such amorphous surfaces [1]. The surface properties of these materials can then be assessed bysimulating small angle scattering, adsorption isotherms, etc. using classical approaches. I willshow how the realistic details of the surface chemistry drastically affects the adsorption of variousfluids such as water, carbon dioxide, methane, hydrogen and their mixtures. Finally, I will alsoconsider the specific case of He and Ne adsorption in dense amorphous silica when subjected tohigh pressures [2]. I will show that a generalized poromechanical approach, describing the elasticproperties of microporous materials upon adsorption, can be applied successfully to silica glass inwhich the free volume exists only at the subnanometer scale. Fig. 1. Atomistic model of micelle-templated mesoporous silicas:Structural, morphological and N2,CO2, H2O adsorption properties.Structural, morphological andadsorption properties of porous silica.The structure and morphology of arealistic model of MCM-41mesoporous silicas are determined bysimulating neutron scattering, X-raydiffraction, electronic microscopy andby calculating chord lengthdistributions, surface area, porousvolume, etc. N2, CO2 and H2Oadsorption are simulated and comparedwith experimental data and theoreticalmodels of adsorption in nanopores. [1] B. Coasne, P. Ugliengo, Atomistic model of micelle-templated mesoporous silicas: structural,morphological and adsorption properties, Langmuir, 28, 11131 (2012). [2] B. Coasne, C. Weigel, A. Polian, M. Kint, J. Rouquette, J. Haines, M. Foret, R. Vacher, B. Ruffle,Poroelastic Theory Applied to the Adsorption-induced Deformation of Vit-reous Silica, J. Phys. Chem. B118, 14519 (2014).0.010.101.0010.00100.00 0.10 1.00 10.00I(Q)(a.u.) Q (Å-1)0.00.10.2