[Ifeffit] problem about negative

Dear all: When I get a wrong fit about Mo-O and Mo-S fit of first two shells. ssO = 0.00729812 # +/- 0.00961052 [0.00300] delrO = -0.02968655 # +/- 0.03378397 [-0.05765] enot = -5.30590978 # +/- 7.08310376 [-16.71557] NO = -1.88450657 # +/- 1.59438947 [0.5] NS = 1.71281926 # +/- 1.08552732 [1.00000] delrS = 0.00418341 # +/- 0.04904499 [-0.05647] ssS = 0.00329415 # +/- 0.00688491 [0.00300] name N S02 sigma^2 e0 delr Reff R ========================================================================== S1.1 1.000 1.456 0.00329 -5.306 0.00418 2.41350 2.41768 O7.1 1.000 -1.602 0.00730 -5.306 -0.02969 1.54660 1.51691 name ei third fourth ========================================== S1.1 0.00000 0.00000 0.00000 O7.1 0.00000 0.00000 0.00000 ssO with a negative coordiantion number NO.I searched the mailist there is only information about negative ss http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg02326.htm... ss to compensate small amp).but here I even get a negative amp.What's wrong can cause a negative amp? Thanks for help. Sincerely, -----原始邮件----- 发件人: "ZHAN Fei" 发送时间: 2014年11月9日 星期日 收件人: ifeffit@millenia.cars.aps.anl.gov 抄送: 主题: [Ifeffit] too small bond length in R space Dear all： I encounter a problem of exafs fit in an example of Mo which have Mo-O Mo-S Mo-Mo bond.The problem is that the Mo-O peak in R space has too small bond length (less than 1.4A(+0.5A for phase correction) ).Because when 1.2>rbkg>0.68 there is little change in spectrum of R and k space,and when I increase the value of rmin of forward Fourier transform the peak changes little,so I think it's not a noise.But when I try to fit it use the 1.35A path of Mo-O,I can't fit it well. Could you give me some advise about fit too small bond length,or recommend papers of similar situation? picture of R space is attached. Thanks Sincerely, zhanfei ihep of China