Electronic structure cluster complexes

Another method for calculating electronic structures of complex surfaces is the cluster calculation. As the electronic state of an atom is mostly affected by the nearest and second-nearest neighbors (Heine, 1980), the results of cluster calculations provide a reasonably accurate account of the electronic states of the top atoms on a surface. Fig. 4.17 is the result of a calculation of W clusters by Ohnishi and Tsukada (1989). 

In the earliest implementation applied to molecular problems, K. Johnson [39] used scattered-plane waves as a basis and the exchange-correlation energy was represented by (13). This SW-Xa method employed in addition an (muffin-tin) approximation to the Coulomb potential of (17) in which Vc is replaced by a sum of spherical potentials around each atom. This approximation is well suited for solids for which the SW-Xa method originally was developed [40]. However, it is less appropriate in molecules where the potential around each atom might be far from spherical. The SW-Xa method is computationally expedient compared to standard ab initio techniques and has been used with considerable success [41] to elucidate the electronic structure in complexes and clusters of transition metals. However, the use of the muffin-tin approximation precludes accurate calculations of total energies. The method has for this reason not been successful in studies involving molecular structures and bond energies [42]. 

Johnson, K. H., 8c Smith, F. C. (1970). Cluster-wave approach to the electronic structures of complex molecules and solids. Physical Review Letters, 24, 139. 

We thank E.S. Giuliano for discussions, suggestions and encouragement. We also acknowledge financial support from Istituto Nazionale di Fisica della Materia (INI, the use of the IBM Power RISC cluster of Centro di Calcolo A. Villari dell Universitlk di Messina (CECUM) and the European HCM Network Ah initio (from electronic structure) calculation of complex processes in materials . 

Electronic structures of transition metal cluster complexes. M. C. Manning and W. C. Trogler, Coord. Chem. Rev., 1981, 38, 89-138 (406). 

The electronic structure of transition metal cluster complexes with weak- and strong-field ligands. G. P. Kostikova and D. V. Korol kov, Russ. Chem. Rev. (Engl. Transl.), 1985,54, 344 (137). 

The relatively broad and featureless absorption spectra of [Fe3S4l clusters belies their complex excited-state electronic structure. This is illustrated in Fig. 5 using P. furiosus 3Fe Fd as an example (42). In addition to the protein band centered at 280 nm, the UV-visible... 

The complexity of the particle size related changes in the cluster geometry and electronic structure renders the results of the theoretical calculations extremely useful when analyzing the experimentally observed trends. 

In compliance with the nuclearity principle, polynuclear clusters are subdivided into a number of other subgroups, e.g. hexanuclear, octanuclear, etc. The binuclear clusters of technetium may be classified according to the electronic structure of their Tc-Tc2 bonds. Then, the d4-d4 complexes with quadruple M-M bonds are the father of all binuclear complexes with Tc-Tc bonds. The addition or removal of electrons from Tc-Tc bonds [1,11] should result in a decrease in the formal multiplicity of M-M bonds. Thus, for instance, the formal multiplicity of Tc-Tc bonds of d3-d3 and d5-d5 binuclear complexes equals3 3, that of d4 d5 and d4-d3 complexes equals 3.5, etc. 

Curioni et al.148 studied the protonation of 1,3-dioxane and 1,3,5-trioxane by means of CP molecular dynamics similations. The dynamics of both molecules was continued for few ps following protonation. The simulation provided a detailed picture the evolution of both the geometry and the electronic structure, which helped to rationalize some experimental observations. CP molecular dynamics simulations were applied by Tuckerman et al.149,150 to study the dynamics of hydronium (H30+) and hydroxyl (OH-) ions in liquid water. These ions are involved in charge transfer processes in liquid water H20 H+. .. OH2 - H20. .. H+-OH2, and HOH. . . OH- -> HO-. . . HOH. For the solvatetd H30+ ion, a picture consistent with experiment emerged from the simulation. The simulation showed that the HsO+ ion forms a complex with water molecules, the structure of which oscillates between the ones of H502 and I L/ij clusters as a result of frequent proton transfers. During a consid-... 

The information available is discussed in light of the effects of excitation energy and the environment on the photofragmentation process of several transition metal cluster complexes. The photochemical information provides a data base directly relevant to electronic structure theories currently used to understand and predict properties of transition metal complexes (1,18,19). 

With respect to calculations of the electronic structure of molecular clusters and their complexes with oxygen, the PM 3 program of the computer-driven system called MOPAC was used. 

In order to explain the catalytic activity of PANI, we have modeled the electronic structure of doped molecular PANI clusters and its adsorption complexes with oxygen and hydrogen. The geometric and electronic... 

In order to study the possible reasons and mechanisms of the catalytic activity of conducting polymers (CP), the electronic structure of some molecular CPs clusters and its adsorption complexes with oxygen were modeled [6], In the CP-O2 complex, the CP surface is an electron density donor. For example, in the case of PANI, the bond orders in adsorbed O2 molecules decrease by about 30%, and the bond lengths L increase by about 24%. Thus, the adsorbed O2 molecules have a fairly high degree of activation and can readily interact with the protons. 

Other electron-poor clusters include the 44-electron Pt3(CO)3(PPh3)4 and the 42-electron species Pd3(CO)3(PPh3)3 and [Re3Cl12p. For the 44-electron system, the 18-electron rule predicts two double bonds within the M3 triangle and for the 42-electron complexes, three double bonds. The structures of the platinum and palladium complexes are unknown, but the Re-Re distances of 2.47-2.49 A in the anion [Re l ]3- are regarded (20) as short and consistent with a formal bond order of two. 

This formula shows a smooth decrease of p toward the bulk magnetic moment with increasing N. However, the experimental results graphed in Figure 1 indicate that the variation of p with N has a more complex, oscillatory behavior. Its explanation requires a detailed consideration of the geometry of the cluster and a better treatment of its electronic structure. 

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