Bulk structure parameters

In (almost) all the theoretical papers the directions of the calculated relaxations agree with the experimentally determined coordinates. The quantitative agreement is not as good as one could expect from state-of-the art ab initio calculations, however. As Harrison et al. pointed out [2], the extensive experience of calculations on bulk oxides which has been built up in recent years leads one to expect that DFT and HF calculations will reproduce experimental bond lengths to somewhat better than 0.1 A. For example, the bulk structural parameters of Ti02 rutile agree better than 0.06A using softcore ab initio pseudopotentials constructed within the EDA, and a plane-wave basis [44]. 

Applications of the quantum methods Although the quantum methods require a much larger computational effort than classical approaches, they have now been applied to as wide a range of systems as the latter. For example, they have been used to describe not only the cohesive properties, such as the bulk structural parameters, the bulk modulus and the electronic structure (Binggeli et al, 1991 Dovesi et al, 1992 Mackrodt... 

Surface crystallography started in the late 1960s, with the simplest possible structures being solved by LEED [14]. Such structures were the clean Ni (111), Cu(l 11) and Al(l 11) surfaces, which are unreconstructed and essentially unrelaxed, i.e. very close to the ideal temrination of the bulk shown in figure B 1.211 a) typically, only one unknown structural parameter was fitted to experiment, namely the spacing between the two outennost atomic layers. 

This method has been applied to water and many other problems with significant success [15, 38 40, 43, 106, 113, 123 127], One worry is that the form of the simulation potential may not be up to the task of producing accurate enough vibrational frequencies. That is, the site parameters of a simulation potential are usually adjusted to give bulk structural or thermodynamic properties of the liquid. In some cases there is a competition, for example, between Lennard Jones and Coulomb interactions such that these liquid properties are given correctly, but the parameters themselves are not completely physical. Thus it is not always clear, for the delicate problem of vibrational frequencies, that this approach will be sufficiently accurate. 

In order to find a reasonable configuration for our calculation, we take test calculation to optimize the bulk structure of pyrite with GGA and LDA exchange-correlation functional. In the calculation, the plane wave cutoff energy set is 280 eV and the key point set is 4 x 4 x 4, the convergence tolerances set is 10 eV/atom. The optimized cell parameter of the two methods is 0.5415 nm and 0.5425 nm respectively, which is in good agreement with the experiment data (0.5417 nm) reported. It indicates that this configuration is sufficient to satisfy the request of accuracy. 

Interfacial structure is known to be different from bulk structure, and in polymers filled with nanofillers possessing extremely high specific surface areas, most of the polymers is present near the interface, in spite of the small weight fraction of filler. This is one of the reasons why the nature of the reinforcement is different in nanocomposites and is manifested even at very low filler loadings (<10 wt%). Crucial parameters in determining the effect of fillers on the properties of composites are filler size, shape, aspect ratio, and filler-matrix interactions [2-5]. In the case of nanocomposites, the properties of the material are more tied to the interface. Thus, the control and manipulation of microstructural evolution is essential for the growth of a strong polymer-filler interface in such nanocomposites. 

Derived values of the structure parameter p for the complex particles formed at the air-water interface were smaller than those for complexes formed in the bulk aqueous solution (see Figure 7.16b and Table 7.3). 

Under reaction conditions solid-state reactions occur that are a function of the temperature and the composition of the reacting gas mixture. In addition, it appears that movement of vacancies, anions, and, possibly, cations occur. Consequently, the catalyst bulk structure is an important parameter in determining activity and selectivity. It follows then that precautions need to be taken in the preparation of the catalyst so that the desired structure can be achieved. 

This chapter deals with the behavior of block copolymer nanostructures subjected to electric fields. We will consider the thin film behavior, elucidate the parameters governing the electric-field-induced alignment, and finally turn to bulk structures and show novel effects of high field strengths on block copolymer... 

Table 5.1 Structural Parameters of Selected Bulk Semiconductors...

In any case, because ion scattering is strongly affected by the thermal vibrations of surface atoms, experimental data must be compared to Monte-Carlo simulations for model surfaces to achieve quantitative results. The available data base for structure-fitting is rather small compared to electron spectroscopies, so the sensitivity to structural parameters is sometimes limited. But when the surface structure is close to the bulk structure, ion channeling data can be strongly sensitive to small variations in structural parameters. 

The parameter c0 measuring the concentration in the first layer adjacent to the core, i.e., in the first layer of the assumed bulk structure, is a convenient parameter for the mathematical description but not a... 

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