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Unexpected direction of Charge Transfer



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?
 
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?
 
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