Vibrational band fractions calculations

Figure 11 2 3. Band structure of MgB2 calculated for the distorted geometry. The displacement of B atoms is f = 0.005/atom (fraction unit) that correspond to 0.032 A0 of B1-B2 bond length elongation for stretching vibration (E2g(a) phonon mode amplitude). At this displacement, the lower splitoff c band has just sank below EF. The Fermi level - EF is indicated by the dashed line. The band structure calculations indicate that dominant is Oi-G2 and Gi-71 bands coupling over the E2g phonon mode...

Figure 11 2 3. Band structure of MgB2 calculated for the distorted geometry. The displacement of B atoms is Af = 0.005/atom (fraction unit) that correspond to 0.032 A° of B1-B2 bond length elongation for stretching vibration (E2g(a) phonon...

The contours of the absorption bands of each of these models were calculated and compared with the experimentally observed shape of the triply degenerates v3 vibration (asymmetrical CH stretching). For completely free rotation (case III) too large a fraction of the over-all intensity would be found in the wings to agree with the experimental curve. Distinction between case I and case II was ambiguous. Case II seemed to fit the experimental curve a little better on the high-frequency side however, this may be due to overlap of another band. 

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