| 10:13:52 AM PST - Thu, Dec 17th 2015 |
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| You need to consider the physics of the situation; you are dealing with an electron that is most likely unbound (or at least very loosely bound). This electron wants to delocalize in space, which the larger, more diffuse basis sets let it do. This is why your frequency keeps decreasing: an electron delocalized over both molecules is not going to show much of an oscillation between the molecules.
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