Electron embedded cluster

The electron density, pj, of the embedded cluster/adsorbate atoms is calculated using quantum chemistry methods (HF, PT, multireference SCF, or Cl). The initial step in this iterative procedure sets to zero,... 

Thus, to the best of our knowledge, there is a lack of embedding cluster studies on the yttrium ceramics where with a sufficient precision both aspects of the ECM were taken in account. In the study [44], we attempted to fill such a gap and carried out the electronic structure calculations of the YBa2Cu307 ceramics at the Moller-Plesset level with a self-consistent account of the infinite crystal surrounding to the quantum cluster. The Gaussian basis set employed (6-31IG) was larger than those used in previous cluster calculations [16,20,22,29]. 

Extensive DFT and PP calculations have permitted the establishment of important trends in chemical bonding, stabilities of oxidation states, crystal-field and SO effects, complexing ability and other properties of the heaviest elements, as well as the role and magnitude of relativistic effects. It was shown that relativistic effects play a dominant role in the electronic structures of the elements of the 7 row and heavier, so that relativistic calculations in the region of the heaviest elements are indispensable. Straight-forward extrapolations of properties from lighter congeners may result in erroneous predictions. The molecular DFT calculations in combination with some physico-chemical models were successful in the application to systems and processes studied experimentally such as adsorption and extraction. For theoretical studies of adsorption processes on the quantum-mechanical level, embedded cluster calculations are under way. RECP were mostly applied to open-shell compounds at the end of the 6d series and the 7p series. Very accurate fully relativistic DFB ab initio methods were used for calculations of the electronic structures of model systems to study relativistic and correlation effects. These methods still need further development, as well as powerful supercomputers to be applied to heavy element systems in a routine manner. Presently, the RECP and DFT methods and their combination are the best way to study the theoretical chemistry of the heaviest elements. 

A very large number of theoretical studies have been performed on MgO and AI2O3. Only some of the early studies and some of the most recent will be described here, in order to give some idea of the extent of progress over the past two decades. Important advances have recently been made in the application of ionic models to such materials as well as in band-theory studies and embedded-cluster studies. After reviewing the early work, contemporary studies of structure, stability, phase relations, and dynamic properties will be described, followed by recent studies of spectral properties and characteristics of the electron-density distribution for each of these materials. Attention is then turned to Si02, the silica polymorphs, and various compounds and clusters that may be used to model tetrahedrally coordinated Si in silica and the silicates. 

Application of the Embedded Cluster Method to the Electronic State of Silicate Glasses... 

Thus we find the embedded cluster method, with a modest number of atoms in the variational space, is very useful to discuss experimental UPS spectra quantitatively and we can get reliable electronic state information on silicate clusters with reasonable computational time. 

Computational studies of dc Carolis et have combined MD simulations of both Ca-doped and undoped CeOz with QM electronic structure calculations of embedded cluster models built from the MD structures. Several interesting aspects were... 

S. P. Greatbanks, I. W. Hillier, N. A. Burton, and P. Sherwood, /. Chem. Phys., 105, 3770 (1996). Adsorption of Water and Methanol on Zeolite Bronsted Acid Sites An Ab Initio, Embedded Cluster Study Including Electron Correlation. 

In this chapter we review the field of electronic structure calculations on metal clusters and nano aggregates deposited on oxide surfaces. This topic can be addressed theoretically either with periodic calculations or with embedded cluster models. The two techniques are presented and discussed underlying the advantages and limitations of each approach. Once the model to represent the system is defined (periodic slab or finite cluster), possible ways of solving the Schrddinger equation are discussed. In particular, wave function based methods making use of explicit inclusion of correlation effects are compared to methods based on functionals of the... 

The discrete variational (DV) Xa method is applied to the study of the electronic structure of silicate glasses in embedded model clusters. The effects of the cluster size, the size of embedded imits, and the Si-0-Si bond angles on the electronic states are discussed. Embeddii units drastically improve the description of the electronic state, when compared to the isolated Si044- cluster, which is the structural unit of silicate glasses e.g., the Fermi energy for the embedded cluster becomes smaller when compared to that of the... 

We have used the DV-Xa embedded cluster method which is explained in detail elsewhere (3,4). Here we give a summary of main feature. The DV-Xa method is based on density functional theory in which the Coulomb and exchange potential energy is a functional of the electronic density. 

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