Atomistic Computer Simulation

Figure 3.10 compares the same experimental data, with a best fit to the Rouse model (Eq. 3.19). Here a good description is observed for small Q-values (Q<0.14 A 0, while at higher Q important deviations appear. Similarly, the simulations cannot be fitted in detail with a Rouse structure factor. Recently this result was confirmed by an atomistic computer simulation on PE molecules of different lengths. Again, at high Q the Rouse model predicts a too-fast decay forSpair(Q,0 [53]. 

Atomistic computer simulations are a statistical mechanical tool to sample configurations from the phase space of the physical system of interest. The system is uniquely treated by specifying the interactions between the particles (which are usually described as being pointlike), the masses of all the particles, and the boundary conditions. The interactions are calculated either on-the-fly by an electronic structure calculation (see Section 2.2.3) or from potential functions, which have been parametrized before the simulation by fitting to the results of electronic structure calculations or a set of experimental data. In the first case, one frequently speaks of AIMD (see Section 2.2.3), although the motion of the nuclei is still treated classically. 

Much more sophisticated models are needed to explicitly deal with the role of the solvent and presumably the only sensible way to make headway here is by means of detailed, that is, atomistic computer simulations. Unfortunately, detailed computer simulations of the self-assembly of large polymeric objects are often not very practical because they require excessive computer processing times, in particular if the solvent molecules are... 

CONTENTS Introduction, Thom H. Dunning, Jr. Electronic Structure Theory and Atomistic Computer Simulations of Materials, Richard P. Messmer, General Electric Corporate Research and Development and the University of Pennsylvania. Calculation of the Electronic Structure of Transition Metals in Ionic Crystals, Nicholas W. Winter, Livermore National Laboratory, David K. Temple, University of California, Victor Luana, Universidad de Oviedo and Russell M. Pitzer, The Ohio State University. Ab Initio Studies of Molecular Models of Zeolitic Catalysts, Joachim Sauer, Central Institute of Physical Chemistry, Germany. Ab Inito Methods in Geochemistry and Mineralogy, Anthony C. Hess, Battelle, Pacific Northwest Laboratories and Paul F. McMillan, Arizona State University. 

In this chapter we show how atomistic computer simulation methods can yield unique insights into the structural properties of amorphous solids. The range and scope of the materials that can currently be studied by modelling techniques is illustrated by recent results, predominantly on glassy materials (defined below), although a brief discussion of other classes of amorphous materials is given towards the end of the chapter. 

Atomistic computer simulation techniques can now provide good structural models of a wide range of glasses. Such models accord well with available experimental data and give new insights into the fascinating structural features of glasses. As computers have become more powerful the size of the models that... 

Cao, Yand Cormaek, A.N. (1995) Insights into the strueture and transport properties of glasses from atomistic computer simulation, imProc. XVI International Congress on Glass Meeting, Beijing China, Oct. 1995. 

Atomistic computer simulation Particle dynamics simulation Molecular modeling... 

Figure 2.3 Apparent distributions of pore size for PIM-1 derived from N2 adsorption at 77 K (9), CO2 adsorption at 273 K (x) and from atomistic computer simulation [221 (bars)...

Three corrosion inhibitors for copper, 3-amino-l,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotiiazole (BTAOH), were investigated by corrosion experiments and atomistic computer simulations [75]. The trend of copper corrosion inhibition effectiveness of the three inhibitors in near-neutral chloride solution was determined experimentally as BTAH > ATA > BTAOH. An exhaustive analysis of the possible interactions between the molecules (in their neutral or deprotonated form) and the surface was done with PBE-D [75]. Physisorption, chemisorption, self-assembly as well as organome-tallic polymer formation attheCu(lll) surface were considered. The results are reported in Table 5.4. 

Finally, an additional complementary modeling approach in the field of SMPs should be mentioned. Usually the necessary material parameters of the theoretical models which are specific to a considered polymer material, such as, e.g.. Young s modulus and thermal expansion coefficient, have to be obtained by experimental measurements. Here, atomistic computer simulations could be used as an alternative. For polyisoprene, Diani and Gall showed in a pioneering paper the principal approach [99] on atomistic modeling of SMPs. 

Atomistic computer simulations are unique in providing a vast amount of detailed thermodynamic information on the properties, which are not readily measured in any experiment. One such property is the bonding energy ... 

The sketch of the possible hierarchy of models is presented in Figure 36. It starts from atomistic computer simulations, which can be coarse-grained by joining several atoms of the same chain into one blob, gaining about 3 orders of magnitude in timescales before the chains start aossing each other. Then a choice has to be made either to coarse-grained further but somehow maintain... 

Cleave AR, Kiiner JA, Skinner SJ, Murphy ST, Grimes RW (2008) Atomistic computer simulation of oxygen ion conduction mechanisms in La2Ni04. SoUd State Ion 179(21-26) 823-826... 

Tabira, Y., Withers, R.L., Minervini, L., and Grimes, R.W. (2000) Systematic structural change in selected rare earth oxide pyrochlores as determined by wide-angle CBED and a comparison with the results of atomistic computer simulation. /. Solid State Chem., 153 (1), 16-25. 

A. J. McDonald and S. Hanna, Atomistic computer simulations of terraced wetting of model 8CB molecules at crystal surfaces. Mol. Cryst Liq. Cryst. 413,135-144 (2004],... 

The molecular mechanism of proton tranter in water was unraveled in the mid-1990s. The recent history is reviewed in Marx (2006). The invention of the Car-Parrinello technique of molecular dynamics (Car and Parrinello, 1985) opened the field of atomistic computer simulations for a myriad of applications in... 

Atomistic computer simulation can be used in a truly predictive capacity to explore new porous architectures and elucidate their properties. In particular, those architectures that are predicted to proffer exemplary catalytic properties can be synthesised. Accordingly, simulation can begin to be used to screen viable nanostructures for important (catalydc) properties. 

Atomistic computer simulation has continued to provide experimenters with unique insights and predictions. However, capturing the hierarchical complexity associated vdth nanomaterials, within a single atomistic model, is difficult perhaps the easiest way to generate such models is by simulating, in part, the synthetic method used during their manufacture. Moreover, a benefit of this approach is the ability to be able to make direct comparisons between experiment and simulation. 

The goal of extending classical thermostatics to irreversible problems with reference to the rates of the physical processes is as old as thermodynamics itself. This task has been attempted at different levels. Description of nonequilibrium systems at the hydrodynamic level provides essentially a macroscopic picture. Thus, these approaches are unable to predict thermophysical constants from the properties of individual particles in fact, these theories must be provided with the transport coefficients in order to be implemented. Microscopic kinetic theories beginning with the Boltzmann equation attempt to explain the observed macroscopic properties in terms of the dynamics of simplified particles (typically hard spheres). For higher densities kinetic theories acquire enormous complexity which largely restricts them to only qualitative and approximate results. For realistic cases one must turn to atomistic computer simulations. This is particularly useful for complicated molecular systems such as polymer melts where there is little hope that simple statistical mechanical theories can provide accurate, quantitative descriptions of their behavior. 

As a whole, McKeown and Budd present criteria for polymers with intrinsic microporosity by using more than 100 monomers."" With the analysis by BET sorption measurement, positron annihilation lifetime spectroscopy and atomistic computer simulation, they emphasized the importance of microporous materials in several applications. 

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