[Ifeffit] problem about negative

ZHAN Fei zhanfei at ihep.ac.cn
Sun Nov 9 07:53:22 CST 2014


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.html(negative 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" <zhanfei at ihep.ac.cn>
发送时间: 2014年11月9日 星期日
收件人: ifeffit at 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















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