Virtual-crystal model

The virtual crystal model gives, for example, for Harrison s homopolar splitting ... 

In a previous work we showed that we could reproduce qualitativlely the LMTO-CPA results for the Fe-Co system within a simple spin polarized canonical band model. The structural properties of the Fe-Co alloy can thus be explained from the filling of the d-band. In that work we presented the results in canonical units and we could of course not do any quantitative comparisons. To proceed that work we have here done calculations based on the virtual crystal approximation (VGA). In this approximation each atom in the alloy has the same surrounding neighbours, it is thus not possible to distinguish between random and ordered alloys, but one may analyze the energy difference between different crystal structures. 

The most elementary assumption which one can make is that adding A and B does not change n E) at all. This is the rigid band approximation, often used in the interpretation of experimental results. It is, in the present case, equivalent to the slightly more sophisticated model defined by the virtual crystal approximation, in which the Hamiltonian is averaged over the ensemble defined by the above probability distribution, to define a periodic Hamiltonian of the form (46), with... 

LCAO matrix. In short, even for a virtual crystal the larger the difference in atomic state energies, the larger the bovraig, as expected from the above arguments. The virtual crystal approximation also leads to parabolic decreases in the density of states around the band edges as in the nearly free electron model. 

How is the binding specificity of the heterodimer achieved compared with the specificity of Mat a2 alone The crystal structure rules out the simple model that the contacts made between the Mat a2 homeodomain and DNA are altered as a result of heterodimerization. The contacts between the Mat o2 homeodomain and DNA in the heterodimer complex are virtually indistinguishable from those seen in the structure of the Mat o2 monomer bound to DNA. However, there are at least two significant factors that may account for the increased specificity of the heterodimer. First, the Mat al homeodomain makes significant contacts with the DNA, and the heterodimeric complex will therefore bind more tightly to sites that provide the contacts required by both partners. Second, site-directed mutagenesis experiments have shown that the protein-protein interactions involving the... 

If structural information of the protein target is available, e.g., a crystal structure, in silico screening of huge virtual compound libraries can be conducted by the use of docking simulations. Based on identified primary hits, structural variations of the ligand can be evaluated by computational modeling of the ligand-protein complex. 

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