Dan, Everyone else... I have two suggestions for optimizing the fit. First, from looking at the crystal structure of the MoS2, I would probably not use the same sigma-squared for all three paths. The crystal structure I looked at online had the Mo connected to various Sulfur atoms, but not directly connected to the other Mo atoms, for example. If this is the case, the motion of the Mo and its neighboring S atoms should be much more highly correlated than the motion of th Mo and the nearest Mo atoms-- So, the Mo-S path should have a smaller debye-waller factor than the Mo-Mo path. Second, you're using alpha*reff for your delr term. Are you sure that the only difference between your model and your actual structure is an isotropic expansion? If bond angles change you won't be able to make that assumption, and from looking at the MoS2 structure, that seems likely. So, in summary, I'd use a different sigma-squared term for each path, and try to make a more sophisticated guess about the form of the delr terms. Hope this helps. Mike Groves On Thu, 28 Oct 2004 dmc@pdx.edu wrote:
Hi Mailing list,
I'm back at fitting commercial Molybdenum Disulfide to a Hexagonal p 63/m m c space group. Although my present fit is reasonable, thanks to the mailing list in August, I was hoping someone might have more suggestions to optimize it. Also, in order to better my fit, I still have seperate e0's, one for the first path, one for the remaining 2 paths. I haven't gotten a satisfactory physical explanation for this and I thought someone might have a good one.
Also, the data on the same sample from two different beamlines seems to be somewhat different, namely the Reduced chi-square is very different (75.6 in one, 636.4 in the other). In both cases I use the first 3 single scattering paths. I may have included too much info, but better too much than too little.
Thank You, Dan Carter
Here are my parameters in both cases, values differ somewhat:
Set: Amp = 0.7 guess: eO ~ 1.57 (1.52) (used for first path) guess: eO_1 ~ -4.77 (2.43) (used for remaining 2 paths) guess: ss ~ 0.0027 (0.000427) guess: alpha ~ -0.004 (0.003255) (positive for second fit) delr_1: alpha*reff
First Fit:
Project title : Fitting merge 10_15_04.chi Comment : Prepared by : Contact : Started : 11:49:36 on 22 October, 2004 This fit at : 11:10:57 on 28 October, 2004 Environment : Artemis 0.7.010 using Windows 2000, perl 5.006001, Tk 800.024, and Ifeffit 1.2.6
============================================================
Independent points = 14.312500000 Number of variables = 4.000000000 Chi-square = 779.303886008 Reduced Chi-square = 75.568861674 R-factor = 0.041210572 Measurement uncertainty (k) = 0.000827712 Measurement uncertainty (R) = 0.022111003 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): e0_1 = -4.7737110 +/- 2.4268840 (guessed as -4.773687 (2.426889)) ss = 0.0027360 +/- 0.0004270 (guessed as 0.002736 (0.000427)) e0 = 1.5684690 +/- 1.5209160 (guessed as 1.568507 (1.520918)) alpha = -0.0040060 +/- 0.0032550 (guessed as -0.004006 (0.003255))
Def parameters: delr_1 = -0.0158980
Set parameters: amp = 0.7
Correlations between variables: e0_1 and alpha --> 0.8622 e0 and alpha --> 0.7870 e0_1 and e0 --> 0.7064 All other correlations are below 0.25
Project title : Fitting merge 10_15_04.chi Comment : Prepared by : Contact : Started : 11:49:36 on 22 October, 2004 This fit at : 11:10:57 on 28 October, 2004 Environment : Artemis 0.7.010 using Windows 2000, perl 5.006001, Tk 800.024, and Ifeffit 1.2.6
============================================================
Independent points = 14.312500000 Number of variables = 4.000000000 Chi-square = 779.303886008 Reduced Chi-square = 75.568861674 R-factor = 0.041210572 Measurement uncertainty (k) = 0.000827712 Measurement uncertainty (R) = 0.022111003 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): e0_1 = -4.7737110 +/- 2.4268840 (guessed as -4.773687 (2.426889)) ss = 0.0027360 +/- 0.0004270 (guessed as 0.002736 (0.000427)) e0 = 1.5684690 +/- 1.5209160 (guessed as 1.568507 (1.520918)) alpha = -0.0040060 +/- 0.0032550 (guessed as -0.004006 (0.003255))
Def parameters: delr_1 = -0.0158980
Set parameters: amp = 0.7
Correlations between variables: e0_1 and alpha --> 0.8622 e0 and alpha --> 0.7870 e0_1 and e0 --> 0.7064 All other correlations are below 0.25
===== Data set >>merge 6_17_04.chi<< ========================================
file: C:\Ifeffit\horae\stash\artemis.project.3\chi_data\merge 6_17_04.chi title lines: Athena data file -- Athena version 0.8.032 Saving merge 6_17_04 (group=merge) as chi(k) . Element=Mo Edge=K Background parameters . E0=20007.492 Eshift=0.000 Rbkg=1.000 . Standard=None . Kweight=2.0 Edge step=0.749 . Fixed step=no Flatten=yes . Pre-edge range: [ -150.000 : -75.000 ] . Normalization range: [ 150.000 : 895.199 ] . Spline range: [ 0.952 : 995.207 ] Clamps: None/Strong Foreward FT parameters . Kweight=2 Window=kaiser-bessel Phase correction=no . k-range: [ 2.000 : 16.100 ] dk=0.00 Backward FT parameters . R-range: [ 1.000 : 3.000 ] . dR=0.00 Window=kaiser-bessel Plotting parameters . Multiplier=1 Y-offset=0.000 . Merge in k space of: ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.101 (mos2_101) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.102 (mos2_102) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.103 (mos2_103) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.104 (mos2_104)
k-range = 2.000 - 13.500 dk = 2.000 k-window = kaiser-bessel k-weight = 2 R-range = 1.000 - 3.000 dR = 0.100 R-window = kaiser-bessel fitting space = R background function = none phase correction = none
R-factor for this data set = 0.74613
Second Fit:
Project title : Fitting merge 10_15_04.chi Comment : Prepared by : Contact : Started : 11:49:36 on 22 October, 2004 This fit at : 11:23:36 on 28 October, 2004 Environment : Artemis 0.7.010 using Windows 2000, perl 5.006001, Tk 800.024, and Ifeffit 1.2.6
============================================================
Independent points = 14.312500000 Number of variables = 4.000000000 Chi-square = 6562.747150466 Reduced Chi-square = 636.387602469 R-factor = 0.032979787 Measurement uncertainty (k) = 0.000181935 Measurement uncertainty (R) = 0.004860095 Number of data sets = 1.000000000
Guess parameters +/- uncertainties (initial guess): e0_1 = -4.0720090 +/- 1.9194040 (guessed as -4.773711 (2.426884)) ss = 0.0046360 +/- 0.0004110 (guessed as 0.002736 (0.000427)) e0 = 1.7659580 +/- 1.1543880 (guessed as 1.568469 (1.520916)) alpha = 0.0010900 +/- 0.0028430 (guessed as -0.004006 (0.003255))
Def parameters: delr_1 = 0.0043250
Set parameters: amp = 0.7
Correlations between variables: e0_1 and alpha --> 0.8416 e0 and alpha --> 0.8045 e0_1 and e0 --> 0.7141 All other correlations are below 0.25
===== Data set >>merge 10_15_04.chi<< ========================================
file: C:\Ifeffit\horae\stash\artemis.project.3\chi_data\merge 10_15_04.chi title lines: Athena data file -- Athena version 0.8.032 Saving merge 6_17_04 (group=merge) as chi(k) . Element=Mo Edge=K Background parameters . E0=20007.492 Eshift=0.000 Rbkg=1.000 . Standard=None . Kweight=2.0 Edge step=0.749 . Fixed step=no Flatten=yes . Pre-edge range: [ -150.000 : -75.000 ] . Normalization range: [ 150.000 : 895.199 ] . Spline range: [ 0.952 : 995.207 ] Clamps: None/Strong Foreward FT parameters . Kweight=2 Window=kaiser-bessel Phase correction=no . k-range: [ 2.000 : 16.100 ] dk=0.00 Backward FT parameters . R-range: [ 1.000 : 3.000 ] . dR=0.00 Window=kaiser-bessel Plotting parameters . Multiplier=1 Y-offset=0.000 . Merge in k space of: ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.101 (mos2_101) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.102 (mos2_102) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.103 (mos2_103) ** C:/USERS/Dan2/raw data MoS2 6_17_04/MoS2.104 (mos2_104)
k-range = 2.000 - 13.500 dk = 2.000 k-window = kaiser-bessel k-weight = 2 R-range = 1.000 - 3.000 dR = 0.100 R-window = kaiser-bessel fitting space = R background function = none phase correction = none
R-factor for this data set = 0.71585
Paths used to fit Both Data Sets, degen, s02 the same. other values different:
F1 p 63/m m c: feff0001.dat .. feff = C:\Ifeffit\horae\stash\artemis.project.3\data0.feff2\feff0001.dat id = reff= 2.4135, nlegs= 2, path= Mo<->S label = r = 2.416130 degen = 6.000000 s02 = 0.700000 e0 = 1.765958 dr = 0.002630 ss2 = 0.004636
F1 p 63/m m c: feff0002.dat .. feff = C:\Ifeffit\horae\stash\artemis.project.3\data0.feff2\feff0002.dat id = reff= 3.1500, nlegs= 2, path= Mo<->Mo label = r = 3.153433 degen = 6.000000 s02 = 0.700000 e0 = -4.072009 dr = 0.003433 ss2 = 0.004636
F1 p 63/m m c: feff0003.dat .. feff = C:\Ifeffit\horae\stash\artemis.project.3\data0.feff2\feff0003.dat id = reff= 3.9683, nlegs= 2, path= Mo<->S label = r = 3.972625 degen = 6.000000 s02 = 0.700000 e0 = -4.072009 dr = 0.004325 ss2 = 0.004636 _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit