# [Ifeffit] Ifeffit and Atoms

Bruce Ravel bravel at anl.gov
Wed Aug 17 12:58:34 CDT 2005

```On Wednesday 17 August 2005 11:37, Angela Beesley wrote:
> Is there anyway to include the spatial group F4-3m in the Atoms or Tkatoms
> list?

Do you mean the space group for the zincblende structure, number 216?
My copy of the international tables says that the symbol for that one
is "F -4 3 m".  I don't see an "F 4 -3 m" in the tables.

> Could you please let me know how to introduce the flatten option using the
> Ifeffit command line?

The following was harvested from Athena's ifeffit buffer.  The macro
is used to make an array with a step function.  The flat_c? parameters
are the difference between the pre- and post-edge line parameters.

## making a step function
macro step x.array x a.step
"Return A.STEP function centered at STEP with X.ARRAY as the x-axis"
n___step = nofx(\$1, \$2)
n___points = npts(\$1)
set t___oss.zeros = zeros(n___step-1)
set t___oss.ones  = ones(n___points-n___step+1)
set \$3 = join(t___oss.zeros, t___oss.ones)
erase n___step n___points
erase @group t___oss
end macro

## make the flattened, normalized spectrum ...
step udvl.energy 8332.7 udvl.theta
set flat_c0=-21.5995647811943 - 1.46770521905781
set flat_c1=0.00579640154058703 - -0.00023480310579162
set flat_c2=-3.65584986262377e-07
set udvl.line = (flat_c0 + flat_c1*(udvl.energy+0) +
flat_c2*(udvl.energy+0)**2)
set udvl.flat = (udvl.pre + (1.8050 - udvl.line)*udvl.theta) / 1.8050
set udvl.fbkg = (udvl.bkg-udvl.preline+(1.8050-udvl.line)*udvl.theta)/1.8050
newplot(udvl.energy+0, "udvl.bkg+0", xlabel="E (eV)", ylabel="x\gm(E)",
fg=black, bg=white, grid, gridcolor="grey82" , xmin=8132.7,
xmax=9132.7, style=lines, color="red", key=bkg, title="x10c.xfs")
plot(udvl.energy+0, "udvl.xmu+0" , xmin=8132.7, xmax=9132.7, style=lines,
color="blue", key="\gm")

> Is there a way that I can write the fitting errors to a file using the
> Ifeffit command line?. For the fitting parameters I usually do write_data
> (......,path1_s02,path1_e0,...) but I would also like to write the errors
> from each fitted value.

The uncertainty in a guess parameter, call it foo, is the scalar
"delta_foo", which you can query ifeffit for.  Uncertainties are not
propagated  through the path parameters in ifeffit.

HTH,
B

--
Bruce Ravel  ----------------------------------- bravel at anl.gov  -or-
ravel at phys.washington.edu
Environmental Research Division, Building 203, Room E-165
Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
Argonne IL 60439, USA                                fax: (1) 630 252 9793

My homepage:    http://feff.phys.washington.edu/~ravel
EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

```