Eigenvectors (Figures)
The intrinsic gap mode eigenvector in the NaI crystal with fcc structure. The mode has a relative amplitude a/d=0.244 (d is the nn distance) and a relative frequency W/W+=0.95. Small circles, Na+ ions; large circles, I- ions.
The panel shows the first harmonic part of the eigenvector, localized on a central light Na+ ion and its neighboring shells with the central Na+ ion vibrating in the [111] direction. The arrows represent 10x actual amplitudes for clarity.
The panel shows the dc part of the eigenvector. The arrows representing the displacements are expanded 40x for clarity. Although not clear from the figure the magnitudes of the dc distortion for the nearest I- ion shell are the same, consistent with an axial distortion around the [111] axis.
The intrinsic gap mode eigenvector for a hypothetical NaI crystal with zinc blende structure. The mode has a relative amplitude a/d=0.116 and a relative frequency W/W+=0.95. Again the central ion vibrates in the [111] direction. Note that although the relative mode amplitude is only one half that of the IGM shown in the previous figure, its relative frequency occurs at the same value in the gap (5.0%) due to the larger elastic distortion in the zinc blende lattice near the mode center. Small circles, Na+ ions; large circles, I-.
The panel shows the first harmonic part of the eigenvector. The arrows represent 20x actual amplitudes.
The panel shows the dc part of the eigenvector. The arrows representing the displacements are expanded 40x.
Last modified: April 3, 1997