Embedded cluster model bond angle

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... 

Figure 1. Structures of the model clusters (a) isolated Si04, (b) embedded Si04 , (c) embedded SisOie, (d) embedded SisOie with second sheath of embedded units, (e) embedded Sii7052 , (f) embedded SisOie with various Si-O-Si bond angles.

For metal surfaces we show, in Figure 1(a), a cluster model for CO on the Cu(lOO) surface. The cluster shown has 9 Cu atoms in the first layer, 16 in the second layer and 9 in the third layer. The CO is placed on an atop site directly above the central first layer Cu atom, and with its molecular axis perpendicular to the surface. The metal-metal distances and bond angles are taken for a (100) face of the face centered cubic, fee, Cu crystal and any relaxation or reconstruction of the surface atoms from perfect bulk geometry is neglected. Furthermore, the cluster is not embedded because it is not easy to describe the chemical influence of surrounding atoms not directly included in the cluster. One way to include the effect of the remainder of the crystal has been used by Whitten... 

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