Embedded-cluster model

Duarte H A and Salahub D R 1998 Embedded cluster model for chemisorption using density functional calculations oxygen adsorption on the AI(IOO) surface J. Chem. Phys. 108 743... 

Fukunishi Y and Nakatsu] H 1992 Modifications for ab initio calculations of the moderately large-embedded-cluster model. Hydrogen adsorption on a lithium surface J. Chem. Phys. 97 6535-43... 

Ellis D E, Benesh G A and Byrom E 1978 Self-consistent embedded-cluster model for magnetic impurities p -NiAl J. Appl. Phys. 49 1543... 

The above methods all assume that a clear spatial distinction can be made between toxic and nontoxic compounds. However, it is sometimes found that toxic compounds form a cluster embedded in a milieu of nontoxic compounds. In such cases, a different technique, embedded cluster modeling, can be used [77]. Cronin [78] has used the technique to model eye irritation data. 

Worth AP, Cronin MTD. Embedded cluster modelling a novel QSAR method for generating elliptic models of biological activity. In Balls M, van Zeller A-M,... 

Adsorption energies relative to desorbed CH, from Cl calculations on CH/ adsorbed at different sites on an embedded cluster model of the Nitlll) surface. A minus sign indicates a repulsive interaction (endothermic relative to gas phase CH ). All CH distances are the same as in CH unless indicated otherwise... 

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... 

Worth, A.P. and Cronin, M.T.D. (1999). Embedded Cluster Modelling - A Novel Method for Analysing Embedded Data Sets. Quant.Struct.-Act.Relat., 18,229-235. 

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... 

Embedded Cluster Models for Electronic States of Silicate Glasses... 

Instead of this type of model, we suggest utilization of TST in the recently developed variational versions (Lauderdale and Truhlar 1985,1986 Truhlar et al. 1986 Truong et al. 1989b). These can be either microcanonical (E-,) or canonical (T) forms. These also include multidimensional tunneling via least-action techniques as well as surface atom motion via embedded cluster models. They do require a PES, but in our opinion, it is preferable to at least indicate a PES rather than make a multitude of assumptions about the dynamics. Because of the speed of the VTST methods, large computing facilities would not be necessary, and a well-documented program exists for these calculations, which should be available by the time of publication of this review (from QCPE at the University of Indiana). 

An obvious candidate for a stable noncyclic carbenium ion is the tert-butyl cation observed in superacidic media. Even if the proton affinity of isobutene (Table 22.1) does not make it very likely that tert-butyl cations will exist in zeolites, several quantum chemical studies have localized stationary points for tert-butyl cations in zeolite and found that they are less stable than the adsorption complex, but are similar in stability to surface butoxides. Because of technical limitations vibrational analysis, which could prove that this cation is a local minimum on the potential energy surface, that is a metastable species, have only recently been made. Within a periodic DFT study of isobutene/H-FER a complete vibrational analysis for all atoms in the unit cell was made [48], and as part of a hybrid QM/MNDO study on an embedded cluster model of isobutene/H-MOR a vibrational analysis was made with a limited number of atoms [49]. Both reached the... 

A comment is due concerning the electrostatic potential above the (001) plane of MgO cluster models. This is a region where adsorbates can be located. Many of them form rather weak bonds with the oxide surface, governed mainly by electrostatics. For Mg +PC embedded cluster models, the electrostatic... 

In the following, we focus on the impact of the gradually improved accuracy of xc functionals and embedded cluster models on the DF observables calculated for single CO molecules on the regular MgO(OOl) surface. As just mentioned. 

The latter findings were corroborated by our further BLYP study of PC-only embedded cluster models [168] that considered three adsorption positions of the regular MgO(OOl) surface for Cu, Ni and Pd single atom adsorbates on-top O , bridge over two adjacent anions, and on-top Mg ". Calculated binding energies of the metal atoms at all three adsorption sites varied by more that 100 kJ/mol for the most strongly bound Ni atom, whereas for a Cu atom, with the weakest interaction with the oxide siuface, this variation was only 15 kJ/mol, i.e. without a clear preference for either on-top 0 or on-top Mg positions. 

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