everal modes.

<br/><i>Options</i>:
<ul>
<li><b>kick_density</b>:  The total density of the system is perturbed.
</li>
<li><b>kick_spin</b>:  The individual spin densities are perturbed differently. Note that this mode
 is only possible if the run is done in spin-polarized mode, or with spinors.
</li>
<li><b>kick_spin_and_density</b>:  A combination of the two above. Note that this mode
 is only possible if the run is done in spin-polarized mode, or with spinors.
</li>
</ul>
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