Dear all, I fit a Zn cluster which RDF has a peak little lower than Zn-S peak,and has a shoulder near Zn-O.This accords with my expection the cluster may have both Zn-S Zn-O bond.But after fit the Zn-O bond length is much larger than reff while it path contribution after fit did in low R.What's wrong with my fit?is it the big delro & delrs =0.7882? sincerely, zhanfei this is the fit log,and puc of fit and path contribution is attached Independent points : 8.0087891 Number of variables : 5 Chi-square : 2276.2312227 Reduced chi-square : 756.5273522 R-factor : 0.0023036 Measurement uncertainty (k) : 0.0002947 Measurement uncertainty (R) : 0.0004735 Number of data sets : 1 Happiness = 100.00/100 color = #D8E796 ***** Note: happiness is a semantic parameter and should ***** ***** NEVER be reported in a publication -- NEVER! ***** guess parameters: enot = 8.99859575 # +/- 1.30831421 [0] ssS = 0.01038392 # +/- 0.00062570 [0.00300] delrS = 0.01271583 # +/- 0.00971686 [0] ssO = 0.02806760 # +/- 0.00277795 [0.00300] delrO = 0.33252269 # +/- 0.01446304 [0] set parameters: amp = 0.85000000 OC = 0.01068708 Correlations between variables: delrs & enot --> 0.9345 delro & enot --> 0.8636 delro & delrs --> 0.7882 sso & enot --> -0.7422 delro & sso --> -0.6014 sso & delrs --> -0.5887 sss & enot --> 0.4980 delrs & sss --> 0.4803 sso & sss --> -0.4737 All other correlations below 0.4 ===== Data set >> CdSe-ZnS(Fe)-Zn << ==================================== : Athena project = C:\04-6-29wulizhu\Zn\athena.prj, 3 : name = CdSe-ZnS(Fe)-Zn : k-range = 3.000 - 10 : dk = 1 : k-window = hanning : k-weight = 1,2,3 : R-range = 1.15 - 3 : dR = 0.0 : R-window = hanning : fitting space = r : background function = no : phase correction = : R-factor by k-weight = 1 -> 0.01310, 2 -> 0.01474, 3 -> 0.02004 name N S02 sigma^2 e0 delr Reff R ========================================================================= O1.1 6.360 0.850 0.02807 8.999 0.33252 1.97800 2.31052 S7.1 3.600 0.850 0.01038 8.999 0.01272 2.34200 2.35472 name ei third fourth ========================================= O1.1 0.00000 0.01069 0.00000 S7.1 0.00000 0.00000 0.00000