Atomistic simulation relationships

Different scale features give different scale properties. At the smallest level, the lattice parameter is a key length scale parameter for atomistic simulations. Since atomic rearrangement is intimately related to various types of dislocations, Orowan [88], Taylor [89], Polyani [90], and Nabarro [91] developed a relationship for dislocations that related stress to the inverse of a length scale parameter, the... 

A central challenge for atomic level simulations of minerals is to be able to model the crystal structure, thermodynamics and atom transport. Clearly, if the same technique is employed then the underlying relationships between these properties can be examined. There are two atomistic simulation techniques that have been used to model these three properties for minerals, lattice dynamics (LD) and molecular dynamics (MD). The aim of this chapter is to describe these techniques and show, via a series of examples, how these methods can be applied. 

Materials Studio is a comprehensive snite of modeling and simulation solutions developed by Accelrys for studying chemicals and materials, including crystal structure and crystallization processes, polymer properties, catalysis, and structure-activity relationships. It offers advanced visnalization tools and access to the complete range of compntational materials science methods [13] and will be applied in the molecn-lar simnlations of the manuscript. The interatomic interactions in Materials Stndio are described by the COMPASS force field (condensed-phased optimized molecnlar potential for atomistic simulation studies) [14]. This is the first ab initio force field... 

Lin, T. S. Atomistic Molecular Dynamics Simulations for the Morphology and Property Relationship of Poly (trimethylene terephthalate) Fiber. PhD Thesis, National Taiwan University (2007). 

The presence of an LLCP and extrema lines in the supercritical region not only affects the thermodynamic properties of the liquid but also affects its dynamics. Recent computer simulations, based on atomistic [41], silica [39], and different water models [41], show that there is an intimate relationship between the C p line and the dynamic properties of the liquids, LDL and HDL. Specifically, it is found that in the more ordered liquid (i.e., the liquid with less entropy), the temperature dependence of the diffusion coefficient at constant pressure is given by D(T) exp(-EAT) (where Ep, is a constant), indicating that such a liquid is Arrhenius [51]. Instead, the less ordered liquid is found to be non-Arrhenius. Interestingly, in the supercritical region of the P-T plane, the dynamics of the fluid... 

Molecular dynamics (MD) is an invaluable tool to study structural and dynamical details of polymer processes at the atomic or molecular level and to link these observations to experimentally accessible macroscopic properties of polymeric materials. For example, in their pioneering studies of MD simulations of polymers, Rigby and Roe in 1987 introduced detailed atomistic modeling of polymers and developed a fundamental understanding of the relationship between macroscopic mechanical properties and molecular dynamic events [183-186]. Over the past 15 years, molecular dynamics have been applied to a number of different polymers to study behavior and mechanical properties [187-193], polymer crystallization [194-196], diffusion of a small-molecule penetrant in an amorphous polymer [197-199], viscoelastic properties [200], blend [201,202] and polymer surface analysis[203-210]. In this article, we discuss MD studies on polyethylene (PE) with up to 120,000 atoms, polyethylproplyene (PEP), atactic polypropylene (aPP) and polyisobutylene (PIB) with up to 12,000 backbone atoms. The purpose of our work has been to interpret the structure and properties of a fine polymer particle stage distinguished from the bulk solid phase by the size and surface to volume ratio. 

Molten silica and its mixtures with various other oxides are of central interest in geosciences, silicates that have formed fix>m such melts in the earth crust are very relevant materials. Such melts are also very important for the glass and ceramics industry, and although both of these materials are in their crystalline and amorphous forms in use for many centuries, the understanding of their structure-property relationship on an atomistic level still poses challenging scientific problems. In recent years, important progress has been made possible by atomistic molecular dynamics simulations, and a selection of problems by this method will be presented below. 

The size effect on the nanosolid melting has been modeled in terms of classical thermodynamics and atomistic MD simulations [31-46]. In general, the size-dependent TinCK) follows the empirical scaling relationship ... 

To conclnde, the present section has highlighted the approaches and limitation to calculating the properties of glass melts. Atomistic and particle simulation can predict the general relationships between composition and properties (e.g., viscosity). Thns, the flnid dynamics models generated will have an implicit description of the underlying chemistry. This enables plant improvements to be made based on a sound chemical and physical nnderstanding. 

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