Crystal Orbital Overlap Population COOP

Density of states (DOS) and crystal overlap population (COOP) for a chain 

Even in more complicated cases it is possible to obtain a qualitative idea. We choose the example of planar PtX4 units that form a chain with Pt-Pt contacts. This kind of a structure is found for K2Pt(CN)4 and its partially oxidized derivatives like K2Pt(CN)4Cl03  

We will consider only the Pt-Pt interactions within the chain in the following. Fig. 10.9 

Formation of bands by interaction of the orbitals of square PtX4-complexes in a polymeric chain and the corresponding band structure and density of states 

10 MOLECULAR ORBITAL THEORY AND CHEMICAL BONDING IN SOLIDS 

At the end of Section 10.1 the Mulliken overlap population is mentioned as a quantity related to the bond order. A corresponding quantity for solids was introduced by R. Hoffmann the crystal orbital overlap population (COOP). It is a function that specifies the bond strength in a crystal, all states being taken into account by the Mulliken overlap populations Its calculation requires a powerful computer however, it can 

At k = the contributions between every other atom are antibonding, and those of 

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Another question is whether the filled orbitals are of a bonding or antibonding character. This is displayed on a crystal orbital overlap population (COOP) plot as shown in Figure 34.3. Typically, the positive bonding region is plotted to the right of the zero line. 

Fig. 10.2 Crystal Orbital Overlap Population (COOP) and Densities of States (DOS) plots for SrCa2ln2Ce (a) COOP plots of the In-In (solid) and In-Ge (dashed) interactions (b) DOS plots of the total DOS (dotted), ln-5py lone pair (dashed), and ln-5px p-states (solid).

The "Crystal Orbital Overlap Population" (COOP) [20] shows (Fig. 4) that all levels arising below the Fermi level are a and Jt bonding and the highest energy levels are ct and n antibonding however the specific COOP curves for each Mo-0 distance (Fig. 5) show a... 

The orbital interaction which is responsible for the adsorption of molecular oxygen on the Ag(110) surface is mainly between silver dxz and 7t 0-0- The interaction between the silver surface and molecular oxygen leads to a donation of 1.55 electrons into the 7t o o from surface because the Fermi level of the surface is located higher in energy than n oo In Figure 1 is shown the contribution for the adsorbed molecular oxygen in 2 to the total density of states (DOS) and also the Ag-O and 0-0 crystal orbital overlap population (COOP) curves. 

Ultimately, the treatment of electronic structure in extended systems is no more complicated (nor is it less so) than in discrete molecules. The bridge to local chemical action advocated here is through decompositions of the DOS and the crystal orbital overlap population (COOP) curves. These deal with the fundamental questions Where are the electrons Where can I find the bonds ... 

Finally, we study the atom-atom and orbital-orbital interactions by evaluation of the crystal orbital overlap population (COOP) and the overlap population (OP) corresponding to bonds and atomic orbitals, in order to analyze... 

Figure 7. Total density of states (DOS) for BaSiNbioOi9 and atomic orbital projections (AOP) for (a) the Nb atoms of the Nb60i2 clusters (b) the Nb atoms of the NbjOn clusters (c) the Nb atoms of the Nb06 octahedra and (d) crystal orbital overlap population (COOP) for the Nb-centered orbitals of the NbjOn clusters.

The formation of C-C chemical bonds in a variety of solids, including some refractory dicarbides, has been considered by Li and Hoffman (1989) and Wijeyesekera and Hoffman (1984) based on EHT (extended Huckel theory) calculations. To our knowledge, these works are the only ones where the band analogues of bond populations, the so-called crystal orbital overlap populations (COOPs) have been calculated for refractory compounds. The most noticeable result is that, in spite of the evident crudeness of the nonself-consistent semiempirical EHT method, the calculations allow us to understand the nature of the phase transition from cubic to hexagonal structure which occurs in the ZrC, NbC, MoC,... series as the VEC increases. The increase of metal-to-metal bonding when going from cubic (NaCl-type) to hexagonal (WC-type) becomes evident. 

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