Mesoscale simulations coarse-grained

The computations required for accurate modeling and simulation of large-scale systems with atomistic resolution involve a hierarchy of levels of theory quantum mechanics (QM) to determine the electronic states force fields to average the electronics states and to obtain atom based forces (FF), molecular dynamics (MD) based on such an FF mesoscale or coarse grain descriptions that average or homogenize atomic motions and finally continuum level descriptions (see Fig. 1). 

An alternative mesoscale approach for high-level molecular modeling of hydrated ionomer membranes is coarse-grained molecular dynamics (CGMD) simulations. One should notice an important difference between CGMD and DPD techniques. CGMD is essentially a multiscale technique (parameters are directly extracted from classical atomistic MD) and it... 

Mesoscale simulation methods [34] bridge between the short length and time scales typically probed by atomistic and coarse-grained simulations at a higher computational cost and the larger scales typically probed by continuum simulations of bulk material behavior. Figure 7.4 is a schematic illustration of length and time scales, adapted from Shelley and Shelley [35]. 

Several attempts have been made to couple microscopic simulations with statistical-mechanical theories. We have demonstrated that the hybrid MC/ RISM technique combining atomistic/coarse-grained MC simulations with integral equation RISM theory is a very effective tool in the computational treatment of equilibrium properties and structural reorganizations in the weak segregation limit, when atomic level information is passed on to mesoscale level. Of course, RISM theory does not predict types of resulting nanostructures or their symmetries. It appears possible, and in fact desirable, to combine RISM or DF formalism with molecular dynamics - both classical... 

As shown in Figure 26.3, both lattice Boltzmann gas (LBG) [37,38], direct simulation Monte-Carlo (DSM-C) [41], and off-grid particle methods such as DPD [42], and fluid particle method (FPM) [43] can be treated within a common methodological framework. This framework in the mesoscale consists the successive coarse-graining of the underlying molecular dynamics system. We can list its components as ... 

Peter C, Deiie Site L, Kremer K (2008) Classical simulations from the atomistic to the mesoscale coarse graining an azobenzene liquid crystal. Soft Matter 4 859-869... 

Particle-based simulation techniques include atomistic MD and coarse-grained molecular dynamics (CG-MD). Accelerated dynamics methods, such as hyperdynamics and replica exchange molecular dynamics (REMD), are very promising for circumventing the timescale problem characteristic of atomistic simulations. Structure and dynamics at the mesoscale level can be described within the framework of coarse-grained particle-based models using such methods as stochastic dynamics (SD), dissipative particle dynamics (DPD), smoothed-particle hydrodynamics (SPH), lattice molecular dynamics (LMD), lattice Boltzmann method (IBM), multiparticle collision dynamics (MPCD), and event-driven molecular dynamics (EDMD), also referred to as collision-driven molecular dynamics or discrete molecular dynamics (DMD). 

The bottom left Panel illustrates models used in dynamic density functional theory (DDFT) simulations (a) The chemical structure of repeat unit of sulfonated poly(ether ether ketone) (sPEEK) chain. Hydrophilic blocks A and hydrophobic blocks B correspond to the sulfonated and nonsulfonated monomers, respectively, (b) The atomistic model of sPEEK chain, (c) The mapping of the atomistic chain onto a coarse-grained [ABtxChain and water molecules onto mesoscale solvent particle of type C. 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

The phase morphology obtained for a simplified DPD model of the PVBPA/PEEK copolymer depends on the way the coarse-grained model is set up. Mutliscale approach was indeed helpful to find the parameters for the mesoscale DPD simulations. 

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