Dear Norbert, Thank you for your reply. About the DW factor, I think the problem may be another scatterer. Due to the self adsoption, I use Dr. Booth's correlation equation to correlate my data. Is that the way I obtain minus DW factor? The other parameters work great, except DW factor for about -0.001(the uncertainties is +/- 0.00094). Do you thinnk is that possible cause by self absorption or other effects? Thank you for your time. Sincerely, Yu-Chuan On Fri, 24 Sep 2004, nobert.weiher@chem.ethz.ch wrote:

Concerning the DW factor, you are right that it accounts for vibrational disorder in the sample (in the ideal case). If, however, your material has a high structural disorder by itself, DW factors might become high due to this. The general behaviour is that they should increase with temperature of the measurement. A negative value is physically not possible, and usually means that something is wrong with your fitting path. Possible things to check are - did you use proper reference paths (i.e. were they correctly computed by feff) - is it maybe another scatterer which contributes to the EXAFS at this part.