Fermi energy orbitals near

However, for this structure, there is a small occupancy of the jt-antibonding obitals near the T-point. Presumably, it is the occupation of these antibonding orbitals which drives the WC to adopt the hexagonal structure. Figure 5.10 shows the calculated bands for this structure. Here the bands near the Fermi energy show a greater degree of jt-character than in the carbides with the NaCl structure. 

Figure 7.6 Representation of crystal orbitals at the zone center that correspond to the energy bands near the Fermi levels in YC2 and Y2C2Br2. (Left) C-C ji band and (right) Yr2- y2 band, dp hybridization is noted in Y2C2BrB.

Bulk M0O2 displays a striking metal-insulator sfructural transition that was the subject of extensive theoretical as well as experimental work. The electronic bulk sfructure was studied by periodic [208] as well as cluster DFT methods [209, 210]. The electronic properties of molybdenum dioxide were found to be dominated by strong hybridization of O 2p and crystal-field split Mo 4d states with bands near the Fermi energy originating almost exclusively from Mo 4d t2g-type orbitals. 

The calculations involved determination of the projected densities of states (ProDOS)(5). The ProDOS were calculated near the Fermi energy, with approximate intensity for dipole allowed transitions from the core levels of selected site and parity. With the one-electron molecular orbitals of the clusters, as in Eq. (5), the ProDOS are defined in terms of the eigenvector coefficients of the orbitals and a Lorentzian (a localized line shape) of width a, as... 

For closed-shell and open-shell molecules, spin-restricted Kohn-Sham (RKS) and spin-unrestricted Kohn-Sham (UKS) density functional calculations were employed, respectively. Except for the calculations of excited states and the cases where pure states are sought, we have employed an approximation in which electron density is smeared among the closely spaced orbitals near the Fermi levels. In this procedure, fractional occupations are allowed for those frontier orbitals with energy difference within 0.01 hartree to avoid the violation of the Aufbau principle (46). 

It is now clearly established that potassium chemisorbed on transition metals functions as an unusually powerful donor. This increases the density of surface electron states available for back-bonding with certain adsorbates, if they possess orbitals with energy and symmetry that correlate near the Fermi energy of the metal. Examples of such orbitals would be the 27t of CO and N2. The important general consequences of this interaction include increased heat of molecular adsorption and increased dissociation probability. 

---