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Re: Unexpected direction of Charge Transfer
Le 17 juin 04, à 08:13, Siew Wei Goh a écrit :
Dear FEFF Users,
I'm hoping someone can help me with a problem which continues to baffle me. It involves charge transfer calculations on Fe, Ni and Co atoms in sulfides, eg. NiS. For some reason, FEFF consistently calculates the charge transfer as negative on the metal and positive on the sulfur counterpart! I do not understand why FEFF does that. Shouldn't S atoms be negative while the metal be positive?
In principle you are right, electrons should be transfered to the S atoms to close their shells. However, this is a principle not a demonstrated rule. There is no reason why it should be like that all the time.
I have tried modifying a number of parameters by changing the degree of muffin-tin radii overlap using either AFOLP or FOLP cards, shifting the Ef relative to DOS using EXCHANGE card as well as using the 5 different available exchange models. None corrected the problem I am facing here. Interestingly, this problem is not observed when dealing with copper and lead sulfides or even in Fe & Ni oxides. Can someone shed light on this behaviour?
Charge transfer is a rather weird parameter, which is not measurable btw. It's value and even sense can depend on its definition. Maybe the best thing to do is to compare FEFF's calculation with some other theory.
Can you cross-check with some other code like LMTO, APW, pseudo-pot or whatever?
If not we can certainly possible to run for you a calculation for reasonably small unit cell.
Cheers
Gilles
Regards
Siew Wei GOH
School of Chemistry
University of New South Wales
Sydney NSW 2052, Australia
Tel: +61 (2) 0385 5519
email: sw.goh@unsw..edu.au
Dr. Gilles Hug
LEM ONERA-CNRS
BP 72
92322 Châtillon
France
+33 1 46 73 45 42
gilles.hug@onera.fr
http://www.onera.fr/visiononera/derniere/laboratoire.html