6.1 Pure Cu example

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6.1 Pure Cu example

Shown below is auto1.inp. This file will need to be copied autobk.inp to run the program. This is about as simple as autobk gets.

 %------------------%    autobk.inp     %-------------------%
 title    = Cu 10K, with standard from feff
 data     = cu10k.dat                   % xmu data
 output   = cu.dat
 standard = cu-feff.chi                 % = chi.dat from feff
 %------------------% end of autobk.inp %-------------------%

The autobk.log you get from this input file should be similar to this:

 --------------------- automatic background removal---------------------
   autobk: version  2.61   17-jan-1995
 -----------------------------------------------------------------------
 Cu 10K, with standard from feff
 --------------------------------------
 input xmu data file name and skey: cu10k.dat  ASCII     
    first document line: Cu foil at 10K                                    
 --------------------------------------
 input theory chi file name and skey: cu-feff.chi  ASCII     
    first document line: Cu metal chi.dat from feff601.a                   
 --------------------------------------
 output chi file : cu.chi
 --------------------------------------
 ----------fitting parameters----------
 initial value of e0        =      8977.580078
 final value of e0          =      8982.461914
 pre-edge range             =       -50.000000     -200.000000
 pre-edge line              =  -.502631E-03 * Energy +   .541864E+01
 edge step                  =         2.302949
 energy range               =      8977.580078    11362.469727
 k range                    =          .000000       24.950001
 k weight                   =         1.000000
   fourier transform window: 
 sills: dk1, dk2            =          .000000         .000000
 # of knots in spline       =    15
 background r range         =          .000000         .981748
 the theory was scaled by   =          .310267
 1st shell r range          =          .981748        2.945243
 -----------------------------------------------------------------------

Don't worry too much if there are slight differences in the actual numbers you get -- precisions vary for different machines. The important numbers are $\ensuremath{E_0}$ (which should be within a few eV of 8982eV), the number of knots in the spline, (which should be exactly 15), and the upper limit of R -range for the background, (which should be 0.98Å, the R -grid point just below 1Å, the default value for $\ensuremath{R_{\rm bkg}}$ ). The edge step and the slope and intercept of the pre-edge line are given (here Energy is the total energy, not relative to $\ensuremath{E_0}$ , in eV). Output data files from this running of autobk will be cuk.chi, containing the $\ensuremath{\chi(k)}$ data, and cue.bkg, containing the $\ensuremath{\mu_{0}(E)}$ data on the same grid as the input data in cu10k.dat.

$\begin{figure} % latex2html id marker 2537 \epsffile{Figs/xmu+bkg.ps} \caption[B... ...bk}}}, using the simple input file of {{{\ttfamily{auto1.inp}}}. }}\end{figure}$

Figure 1 shows the low energy part of the the original $\ensuremath{\mu(E)}$ and the $\ensuremath{\mu_{0}(E)}$ function. Note that there is a large spike in the $\ensuremath{\mu_{0}(E)}$ function at very low energy. Such spikes at low-energy are not unusual from autobk, but do not cause much of a problem. In this case, the entire spike is below 1 $\ensuremath{{\rm\,\AA^{-1}}}$ , which does not get very much weight in a Fourier transform into R -space, and so is not very important in the fit done by autobk. Such spikes do imply that the autobk method may not be optimal for getting near-edge structures, but that's another story. The resulting $\ensuremath{\chi(k)}$ data is shown in Fig. 2, which looks quite good even at low-k , the hard part of background removal. The Cu data actually extends reliably out to about 22 $\ensuremath{{\rm\,\AA^{-1}}}$ .
$\begin{figure} % latex2html id marker 2557 \epsffile{Figs/chi.ps} \caption[Resul... ...tobk}}}, using the simple input file of {{{\ttfamily{auto1.inp}}}}}\end{figure}$

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