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June 16, 2005
Work at the Lee Group
For those of you who know me, you’ve probably either figured out by now or have had me tell you that I am in Ithaca (at Cornell University) doing x-ray crystallography and research on gallium (III) phthalocyanine hydroxide form I, a compound related compositionally to form V, which is used as a discharge agent in high-end Xerox photocopiers. The interesting thing is that whereas form V discharges very quickly, form I does not possess this property. The only difference between forms I and V is their crystal structure. I am trying to find the crystal structure of form I (form V is already known).
Now, what I have done is go through the Cambridge Structure Database and select all relevant (and similar phthalocyanine compounds) and use a program known as Cerius2 to calculate a theoretical x-ray diffraction powder pattern. This powder pattern is compared to the given powder pattern from Xerox (the company that is paying me, in a manner of speaking) and similarities noted. The interesting thing about crystal structures is that it is not the actual atoms that change a powder pattern, but their relative orientations. So I have taken the structures of the known phthalocyanines and edited them so that they correspond to those of HOGaPc-Form(I) (you take a guess as to what that stands for).
The next part involves running something called a VASP calculation on the modified structure. This calculation essentially attempts to minimize the sum of the kinetic and potential energies of the electrons in the structure. The tricky part is that the position of the electrons isn’t known, so there’s something akin to a recursion in the calculations for potential energy. Anyway, out comes the output and we refine the calculation again and again.
Results yet to come…
Posted by aSo at June 16, 2005 05:58 PM