[Ifeffit] Fwd: FEFF trouble help me please !!!!

Bruce Ravel bravel at bnl.gov
Tue Jul 7 16:00:55 CDT 2015


I want to remind everyone that it is important to use the mailing
list.  I do not feel that I am obligated to answer questions about the
software that come to me by any other channel, particularly when I do
not have a personal relationship with the person asking the question.
That said, I am forwarding this fellow's question to the mailing list
and providing an answer.

Thitipong, this is a case of GIGO.

According to Acta Cryst. (1972). B28, 3102-3103 (the reference I found
for Cr23C6):

   The crystal structure of chromium carbide, C r 2 3 C 6 , has
   been described as cubic, space group Fm3m, 4Cr (I) in (a)
   (000), 8Cr (II) in (c) (l-lq:), 48Cr (III) in (h) (Oxx), x=
   0.165, 32Cr (IV) in (f) (xxx), x=0.385, 24C in (e) (x00),
   x=0-275 (Westgren, 1933) on the basis of X-ray single
   crystal and powder diffraction data. We have confirmed
   this structure and determined the atom positions more
   precisely by a neutron diffraction study of a powder sample.

Using those coordinates, I have no problem running atoms and feff.
The structure is a bit strange -- I guess this is more like a metal
than a carbide -- but it seems consistent with the paper after a
cursory inspection.

According to http://www.crystallography.net/cod/1009019.html, the
space group for Cr7C3 is P M C N.  Atoms and feff run fine with this
input data.

Some hints on asking questions that so you'll get the answers you are
looking for:



-------- Forwarded Message --------
Subject: 	FEFF trouble help me please !!!!
Resent-Date: 	Fri, 3 Jul 2015 04:25:57 +0000
Resent-From: 	bruce.ravel at nist.gov
Date: 	Fri, 3 Jul 2015 11:33:12 +0700
From: 	Thitipong Po-Kloy <thitipong_37 at hotmail.com>
To: 	bruce.ravel at nist.gov <bruce.ravel at nist.gov>

Hi Bruce ,
My name is Thitipong . I have trouble about FEFF program and believes
   you can help me.
Now I am doing "XANES simulation" Cr23C6 and Cr7C3 .
So , when I run FEFF program - it report TWO ATOMS VERY CLOSE TOGETHER .
How can I fix it ?

This it Data of atom Cr23C6

title name :    Cr23C6
title formula : Cr23C6
space F M 3 M
a=10.6599 b=10.6599 c=10.6599
rmax = 10
Cr  0     0     0     Cr1
Cr  0.25  0.25  0.25  Cr2
Cr  0.385 0.385 0.385 Cr3
Cr  0     0     0.340 Cr4
C   0.276 0.276 0.276 C1

and Cr7C3

title name :    Cr7C3
title formula : Cr7C3
space P M C M
a=7.0149 b=12.1530 c=4.5320
rmax = 10   rpath=6
Cr  0.064  0.811  0.056 Cr1
Cr  0.250  0.626  0.057 Cr2
Cr  0.250  0.206  0.250 Cr3
Cr  0.250  0.416  0.261 Cr4
Cr  0.065  0.021  0.250 Cr5
C   0.250  0.562  0.459 C1
C   0.029  0.342  0.028 C2

If there is any other way please let me know.

Thank You ,

  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 535A
  Upton NY, 11973

  Homepage:    http://bruceravel.github.io/home/
  Software:    https://github.com/bruceravel
  Demeter:     http://bruceravel.github.io/demeter/

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