Band theoiy

Band Theoiy of Solids. The outer electrons of the atoms in a crystal lattice behave as though unbound, but subject to a periodic electrical potential corresponding to the lattice spacing. Their possible energies fall into bands of allowed and forbidden states. See also... 

The chapter summarizes the results of recent studies from our laboratories aiming at the development of a chemist-oriented approach to the description of the structures and bonding of the solid state. The main motivation for these efforts originates from the fact that traditional physicist s approach to the description of the solid state in terms of band theoiy considerably differs from tbe more intuitive but remarkably... 

If the regular periodicity of their atoms is taken into account, the reflectance characteristics of metals can also be understood in terms of the same molecular oibital theoiy that apphes to organic colorants. In this case it serves as a more fundamental basis for band theoiy, in terms of which the optical and electrical conductance properties of metals and semiconductors have classically been characterized. 

Since shallow-level impurities have energy eigenvalues very near Arose of tire perfect crystal, tliey can be described using a perturbative approach first developed in tire 1950s and known as effective mass theoiy (EMT). The idea is to approximate tire band nearest to tire shallow level by a parabola, tire curvature of which is characterized by an effective mass parameter m. ... 

An impressive application of infrared and Raman spectroscopy was demonstrated in studies of superelectrophilic diprotonated thiourea, [H3NGSH jNfE 2+ 2AsFf,. The Raman spectrum (taken at — 110°C) corresponded reasonably well with calculated vibrational bands predicted by density functional theoiy.38 Coupled with computational methods for predicting vibrational frequencies, it is expected that vibrational spectroscopic techniques will be useful for the observations of these and other superelectrophiles. 

The second method, known as the electronic method, is based on the theoiy of energy bands of the solid and uses free electrons or electron holes of the solid. An electron or a hole is exchanged between the adsoibate and the adsorbent as a whole (at least the whole of the surface). This is then a delocalized approach with an electron. The model no longer takes into account the identification of the site of adsorption. 

---