Special features of "bloch"
You may also want to look at the full parameter list of all the buttons and sliders, or at one of the general help files, Sliders, or
Graphs.
Functionality
- calculate bands gives a display on the right of the energy band structure, for the range of energies between Emin and Emax entered below the graph, for the periodic potential with parameters as specified by the sliders.
- calculate psi gives in the left display three alternative representations of the wave function for the energy specified by energy in the central panel. The three dimensional representation of psi may be rotated by dragging in the display with the cursor, and returned to the reference orientation (looking along the z-axis) by a click with the right mouse button. For more details, check out the full parameter list.
Key equivalents
- calculate bands: use the i-key
- calculate psi: use the spacebar, or double click on the band diagram at the desired energy.
Gap states
- For the reference orientation of the axes in the 3-D psi plot (looking along the z-axis), a gap state, being pure real doesnÕt show. Tilt the axes and youÕll see it.
Narrow bands
- Band widths can become exponentially small and give "bloch" a hard time. If you want to resolve a narrow band, the best bet is to reduce the range Emax - Emin once, or even several times, since the program resolution is set by this range, together with the resolution parameter in the configure dialog.
- In its effort to find narrow bands, "bloch" occasionally reports non-existent ones. These usually appear at moderate energies where the legitimate bands have substantial breadth. Ignore any absolutely flat bands that appear in this range. They usually disappear if the energy range is slightly changed.
- In its search for narrow bands, "bloch" may exceed the number of trial cycles it is allowed. If this occurs, the band diagram develops a few random straight lines at high energy which are meaningless. Ask for a smaller range of energies Emax - Emin or, in the configure dialog, for lower resolution.
band list
- The band list is occasionally confused and separates a single band into two pieces. Watch out for two successive bands with the same band index--they're really two pieces of the same band.
- Occasionally the band index will be incorrectly given in the band list.
NO UPDATE warning
- The band structure and wave function do not automatically update when parameters are changed: the calculate buttons (or key equivalents) must be pressed. There is NO warning signal that parameters have been changed since the latest calculate!
BUG
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If you choose Emax = -Emin, then a band at zero energy will show a glitch at zero energy which is pure artifact: ignore it.