Addressing Surface Effects at the Particle-Continuum Interface in a Molecular Dynamics and Finite Elements Coupled Multiscale Simulation Technique

Y Jain and M Ries and S Pfaller and F Muller-Plathe, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 18, 2375-2387 (2022).

DOI: 10.1021/acs.jctc.1c00940

Atomistic-to-continuum coupling methods are used to unravel molecular mechanisms of polymers and polymercomposites. These multiscale techniques advantageously combine the computational efficiency of continuum approaches whilekeeping the accuracy of particle-based methods. The Capricciomethod Pfaller et al.Comput. Methods Appl. Mech. Eng.2013,260,109-129. is a well-proven multiscale technique, which connectsfinite elements (FE) with molecular dynamics (MD) in apartitioned-domain approach. A vital aspect of these multiscalemethods is to provide physically sound boundary conditions to theparticle domain suppressing any interface effects at the domainboundary occurring due to the coupling. These interfacial couplingartifacts still pose a significant problem, especially for amorphouspolymers due to their highly irregular microstructure. We solve this problem by extending the particle-continuum interface by a layerof passive atoms which move with the outer continuum, thereby providing the missing interactions with a surrounding polymer bulkto the inner particle region. This solution allows us to successfully reproduce structural and mechanical properties obtained underconventional periodic boundary conditions, like density, stress, Young's modulus, and Poisson's ratio. Furthermore, we demonstratethe application of a nonaffine deformation by means of a simple bending test. In general, our revised method provides a frame workto apply complex deformations for molecular scientists, while it allows the engineering community to examine challenging phenomena such as fracture behavior at a molecular level

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