[GSAS-II] Cagliotti parameters on a Si standard, U -> negative

[Andrea Bianchi]

Dear GSAS-II mailing list,

I have a curious problem, in that I was trying to refine the powder x-ray of Si standard. However, when I try to do this, the U parameter goes negative, while it is supposed to be a positive number. This even happens when I start with 10,5, and 2 as starting parameters for U, V, and W and try to refine them sequentially.

Is there a good explanation for this behavior? Am I doing something wrong?

Thank you for your help,

Andrea


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Prof. Andrea Bianchi
Département de physique
Université de Montréal
Complexe des sciences
B-4421
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Montréal (Québec)  H2V 0B3
Canada

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