Greetings! I have inherited a vanadium EXAFS data set (due to a group member graduating - lucky dog!) that is giving me major fits. I am getting consistent numbers with all my fits which visually look fantastic, that is until I look at the numbers...one Debye-Waller factor is negative (a V-O path) and the Eo's are large, the V-Cl path is on the order of -20 eV, the V=O path is on the order of 17 eV, and the V-O path falling at -11 eV. ARe there any "tricks" outside of restraints or constraints that I can attempt to get more realistic values? (I understand that a large Eo can be realistic, but a negative Debye-Waller factor doesn't make sense.) I can restrain the V-O Debye-Waller factor and get a positive value, but then the V=O D-W factor is negative. If I restrain both D-W factors, the fit falls apart, suggesting something else is wrong that I just can't find. Another issue I'm having involves something in Artemis that's confusing me. Sometimes after a fit, the Artemis Pallet shows the V=O feature as the one at 1.8 Angstroms and the V-O feature at 1.6 Angstroms, completely reversed to the FEFF model. I have seen this when I separated the chlorides as well (I attempted to model the Cl at different distances as reported by Deguns, et. al. (attached) due to the immediate environment around the V in our sample being similar to the one they report in scheme 1-(I), p5008). Attached is a text file that shows an Artemis Pallet output illustrating what I'm trying to describe for the V=O and V-O paths. The Artemis project that generated the output is also attached. At this point, I'm wandering what I'm missing. Any help is greatly appreciated!! Many thanks in advance! Rich Mayes Barnes Group 450/452 Buehler Hall Dept. of Chemistry Univ. of Tennessee Knoxville, TN 37996 Project title : Fitting SA_162deglitch-merge.chi Comment : Fit #1 Prepared by : Contact : Started : 15:46:44 on 17 April, 2007 This fit at : 15:58:01 on 18 April, 2007 Environment : Artemis 0.8.007 using Windows XP, perl 5.006001, Tk 800.024, and Ifeffit 1.2.9 Figure of merit : 3 ============================================================ Independent points = 14.027343750 Number of variables = 9.000000000 Chi-square = 45.640992098 Reduced Chi-square = 9.078550099 R-factor = 0.012557807 Measurement uncertainty (k) = 0.000687372 Measurement uncertainty (R) = 0.023895029 Number of data sets = 1.000000000 Guess parameters +/- uncertainties (initial guess): enot = 17.1999060 +/- 3.4058600 (0.0000) delr = 0.1588460 +/- 0.0081480 (0.0000) ss = -0.0022720 +/- 0.0007180 (0.0030) enot_O2 = -11.0384940 +/- 9.8688920 (guessed as enot) delr_O2 = -0.2214820 +/- 0.0356500 (0.0000) ss_O2 = 0.0027560 +/- 0.0021290 (0.0030) enot_Cl = -16.0026700 +/- 3.5982940 (guessed as enot) delr_Cl = -0.0118230 +/- 0.0104780 (0.0000) ss_Cl = 0.0016470 +/- 0.0004220 (0.0030) Set parameters: amp = 0.93 CN_O1 = 1 CN_O2 = 1 CN_Cl = 2 Correlations between variables: enot_Cl and delr_Cl --> 0.9479 enot_O2 and delr_O2 --> 0.9104 enot and enot_Cl --> 0.8766 enot and enot_O2 --> -0.8755 ss and delr_Cl --> 0.8737 delr_O2 and enot_Cl --> -0.8655 ss and enot_Cl --> 0.8469 enot_O2 and enot_Cl --> -0.8220 ss and delr_O2 --> -0.8025 enot and delr_Cl --> 0.7864 enot and delr_O2 --> -0.7825 delr_O2 and delr_Cl --> -0.7817 enot_O2 and ss_O2 --> 0.7535 delr_O2 and ss_O2 --> 0.7259 enot_O2 and delr_Cl --> -0.7080 ss and enot_O2 --> -0.6872 enot and ss --> 0.6795 delr_O2 and ss_Cl --> -0.6271 delr and ss_Cl --> -0.6217 ss_O2 and enot_Cl --> -0.6173 ss and ss_Cl --> 0.5740 ss_O2 and ss_Cl --> -0.5640 enot and ss_O2 --> -0.5314 enot_Cl and ss_Cl --> 0.5264 ss and ss_O2 --> -0.5084 enot_O2 and ss_Cl --> -0.4750 ss_O2 and delr_Cl --> -0.4747 delr_Cl and ss_Cl --> 0.4701 delr and ss_O2 --> 0.4134 enot and delr --> 0.3090 enot and ss_Cl --> 0.2693 All other correlations are below 0.25 ===== Data set >>SA 162deglitch-merge<< ======================================== file: C:\Program Files\Ifeffit\horae\stash\artemis.project.2\chi_data\SA_162deglitch-merge.chi title lines: Self absorption correction of 162deglitch-merge using method of Troger et al. + V K edge + Formula=H24.75 C8.25 O21.48 Si12.125 Cl4.7 V1.48 Merge in e space of: ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.001 ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.002 ** D:/200600603/Barnes-lab/EXAFS/NSLS/EXAFS/MYL-JULY-2006/all-VOCl3/162-Me2SiCl2+V5/162.003 k-range = 2.388 - 15.000 dk = 2.000 k-window = hanning k-weight = 2 R-range = 1.200 - 3.000 dR = 0.200 R-window = hanning fitting space = R background function = none phase correction = none R-factor for this data set = 0.01256 ===== Paths used to fit SA 162deglitch-merge FEFF1: Path 1: [O] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0001.dat id = reff= 1.6819, nlegs= 2, path= V<->O label = r = 1.840746 degen = 1.000000 s02 = 0.930000 e0 = 17.199906 dr = 0.158846 ss2 = -0.002272 3rd = 0.000000 4th = 0.000000 ei = 0.000000 FEFF1: Path 2: [O] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0002.dat id = reff= 1.8269, nlegs= 2, path= V<->O label = r = 1.605418 degen = 1.000000 s02 = 0.930000 e0 = -11.038494 dr = -0.221482 ss2 = 0.002756 3rd = 0.000000 4th = 0.000000 ei = 0.000000 FEFF1: Path 3: [Cl] .. feff = C:\Program Files\Ifeffit\horae\stash\artemis.project.2\data0.feff1\feff0003.dat id = reff= 2.1121, nlegs= 2, path= V<->Cl label = r = 2.100277 degen = 1.000000 s02 = 1.860000 e0 = -16.002670 dr = -0.011823 ss2 = 0.001647 3rd = 0.000000 4th = 0.000000 ei = 0.000000