Molecular orbital cluster method

The local lattice instability by the hole-doping has been smdied by the molecular orbital cluster method [15]. In this method a part of a solid, cluster , is embedded in a model potential that mimics the crystal environment and the molecular orbital calculation is only performed on the cluster. The advantage of this method is that strong-electron correlation is systematically handled. However, the cluster size is rather limited, thus, a care must be taken whether it really reflects the bulk property. 

A different approach was taken by Hao and Cooper (1994), who used a combination of the him linear muffin-tin orbital (LMTO) method and an ab initio molecular quantum cluster method, to investigate S02 adsorption on a Cu monolayer supported by 7—AI2O3. Emphasis here was on the geometry of adsorption sites, with the conclusion that the preferred adsorption site is the Al—Al bridging one. 

The DV-Xx cluster method [11], which is one of the first principle molecular orbital calculation methods, was used for the calculation of the electronic state of the Li3N crystal. In this method, Slater s exchange potential was used [12],... 

The DV-Xa cluster method is a molecular orbital calculating method, assuming a Hartree-Fock-Slater (HFS) approximation. In this calculation, the exchange-correlation between electrons, is given by the following Slater s Xa potential. 

In the present work, we have calculated the K/3 /Koc x-ray intensity ratios for 3d transition elements excited by PI and EC, taking into account both effects described above. The calculations were made using the discrete-variational (DV) X(X molecular orbital (MO) method (19). The electronic states and wave functions in molecules were obtained for tetrahedral (Td) and octahedral (Oh) clusters. The x-ray emission rates were estimated by the DV integration method (20) with the MO wave functions in the dipole approximation. The calculated results are compared with the experimental data. 

In 1976 Leban et used this approach to study the interaction of a platinum electrode with several particles, among them the water molecule and halide ions. The cluster used was taken to be a model of the Pt( 111) surface and contained only five platinum atoms. In this work the iterative extended Huckel molecular orbital (lEHT) method was used. The stability of the adsorption of the water molecule and of the ions was tested by computing the charge transfer to the cluster and the total energy of the system for various positions of the adsorbate on the surface. 

This review concentrates on the fundamentals of supermolecule model chemistries for clusters of atoms/molecules held together by weak chemical forces. The principles behind the appropriate selection of theoretical method and basis set for a particular class of weak noncovalent interactions provide the foundation for understanding more complex computational schemes that might require the user to specify more than just a method and/or basis set, such as highly efficient fragmentation schemes [e.g., the effective fragment potential (EFP) method, " the fragment molecular orbital (FMO) method, the... 

Only the structures of di- and trisulfane have been determined experimentally. For a number of other sulfanes structural information is available from theoretical calculations using either density functional theory or ab initio molecular orbital theory. In all cases the unbranched chain has been confirmed as the most stable structure but these chains can exist as different ro-tamers and, in some cases, as enantiomers. However, by theoretical methods information about the structures and stabilities of additional isomeric sul-fane molecules with branched sulfur chains and cluster-like structures was obtained which were identified as local minima on the potential energy hypersurface (see later). 

As holds for other cluster systems, certain magic cluster electron counts exist, which indicates for a certain cluster-halide ratio and interstitial present the filling of all bonding molecular orbitals and therefore the thermodynamically most stable situation. For main group interstitial atoms these are 14 cluster-based electrons whereas for transition-metal interstitials the magic number is 18 [1, 10-12]. All of these phases are synthesized by high-temperature solid-state chemical methods. A remarkable variety of different structure types has been... 

However, due to the availability of numerous techniques, it is important to point out here the differences and equivalence between schemes. To summarize, two EDA families can be applied to force field parametrization. The first EDA type of approach is labelled SAPT (Symmetry Adapted Perturbation Theory). It uses non orthogonal orbitals and recomputes the total interaction upon perturbation theory. As computations can be performed up to the Coupled-Cluster Singles Doubles (CCSD) level, SAPT can be seen as a reference method. However, due to the cost of the use of non-orthogonal molecular orbitals, pure SAPT approaches remain limited... 

Although Ni(CO)4 was discovered many years ago, no neutral Ni2(CO)x compound has ever been synthesized in macroscopic amounts. However, several communications report ionic species such as [Ni2(CO)8l+, [Ni2(CO)7], and [Ni2(CO)6]+, where structures with one or two bridging carbonyls are proposed.2418 Plausible structures for neutral Ni2(CO)x (x = 5, 6, 7) have been investigated by theoretical methods, and decomposition temperatures well below room temperature have been predicted.2419,2420 Tetra-, penta-, and hexanuclear nickel carbonyl clusters have been investigated by means of molecular orbital theory. It is found that the neutral forms are more stable than the corresponding anionic forms but the anionic forms gain in stability as the nuclearity rises.2421 Nickel carbonyl cluster anions are manifold, and structural systematics have been reviewed.2422,2423 An example includes the anion [Ni9(CO)i6]2- with a close-packed two-layer metal core.2424... 

Quantum-chemical cluster models, 34 131-202 computer programs, 34 134 methods, 34 135-138 for chemisorption, 34 135 the local approach, 34 132 molecular orbital methods, 34 135 for surface structures, 34 135 valence bond method, 34 135 Quantum chemistry, heat of chemisorption determination, 37 151-154 Quantum conversion, in chloroplasts, 14 1 Quantum mechanical simulations bond activation, 42 2, 84—107 Quasi-elastic neutron scattering benzene... 

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