[Ifeffit] Node in chi(k) envelope for a single shell

Wayne Lukens wwlukens at lbl.gov
Mon Nov 6 10:46:48 CST 2006


Dear Silvio,

I was not able to view the image, but what you are describing seems like
the Ramsauer-Townsend effect (Phys Rev B, 1988, V38, 10919–10921).

As far as I understand it, the physical interpretation is that the at  
the
energy of the dip, the potential well of the scattering atom has cross-
section that is very close to the wavelength of the photoelectron.   
Consequently,
the photoelectron is not scattered back to the absorbing atom  
efficiently
at this energy.  Perhaps someone in the list can explain this more
clearly (or correctly).

Sincerely,

Wayne Lukens
On Nov 5, 2006, at 4:38 AM, levy at msri.org wrote:

> Dear List,
>
> I have noticed in several fits that Artemis -- i.e., feff -- reports  
> for
> a SINGLE shell (with absorber = scatterer = Hg, edge = L3) an  
> almost-node
> in the envelope of chi(k) around 6 inverse angstroms. See the image at
>
> http://pjm.math.berkeley.edu/users/levy/files/HgNode.gif
>
> and the FEFF output after my signature.
>
> I've done my best to account for this behavior, but I simply don't
> have a physical intuition for why the F(k) factor should dip to zero
> or almost zero.  Note that this is not a beat caused by two similar
> frequencies being added; the Fourier transform does
> of course show two peaks -- which is how my curiosity was aroused --
> but the example figure comes from a SINGLE path, with 12 identical
> scatterers all at the same distance from the absorber.
>
> Looking forward to your two cents...
>
> Silvio
>
>
>
> Metacinnabar from CSDWeb, HgS Niculescu et al. 1970    Feff 6L.02     
> potph
> 4.12
>  Abs   Z=80 Rmt= 1.327 Rnm= 1.667 LIII shell
>  Pot 1 Z=16 Rmt= 1.218 Rnm= 1.515
>  Pot 2 Z=80 Rmt= 1.310 Rnm= 1.624
>  Gam_ch=5.000E+00 H-L exch
>  Mu=-2.727E+00 kf=1.809E+00 Vint=-1.519E+01 Rs_int= 2.005
>  Path    2      icalc       2                           Feff 6L.02
> genfmt 1.4\4
>   
> ----------------------------------------------------------------------- 
> -------\-
>    2  12.000   4.1366    2.9707   -2.72701 nleg, deg, reff,  
> rnrmav(bohr),
> edge
>         x         y         z   pot at#
>      0.0000    0.0000    0.0000  0  80 Hg       absorbing atom
>      0.0000   -2.9250   -2.9250  2  80 Hg
>     k   real[2*phc]   mag[feff]  phase[feff] red factor   lambda
> real[p]@#
>   0.000  5.8876E+00  0.0000E+00 -5.3100E+00  0.1085E+01  5.5410E+00
> 1.8179E+00
>   0.200  5.8828E+00  6.5887E-02 -6.9020E+00  0.1085E+01  5.5726E+00
> 1.8284E+00
>   0.400  5.8685E+00  1.3063E-01 -8.3679E+00  0.1084E+01  5.6628E+00
> 1.8594E+00
>   0.600  5.8452E+00  1.9388E-01 -9.7059E+00  0.1082E+01  5.7987E+00
> 1.9101E+00
>   0.800  5.8135E+00  2.5592E-01 -1.0913E+01  0.1079E+01  5.9607E+00
> 1.9793E+00
>   1.000  5.7742E+00  3.1673E-01 -1.1989E+01  0.1077E+01  6.1257E+00
> 2.0656E+00
>   1.200  5.7279E+00  3.7510E-01 -1.2932E+01  0.1075E+01  6.2715E+00
> 2.1679E+00
>   1.400  5.6750E+00  4.2855E-01 -1.3742E+01  0.1074E+01  6.3832E+00
> 2.2854E+00
>   1.600  5.6157E+00  4.7354E-01 -1.4416E+01  0.1075E+01  6.4589E+00
> 2.4174E+00
>   1.800  5.5491E+00  5.0618E-01 -1.4949E+01  0.1076E+01  6.5142E+00
> 2.5639E+00
>   2.000  5.4733E+00  5.2301E-01 -1.5329E+01  0.1077E+01  6.5837E+00
> 2.7250E+00
>   2.200  5.3844E+00  5.2240E-01 -1.5543E+01  0.1078E+01  6.7192E+00
> 2.9013E+00
>   2.400  5.2972E+00  5.4699E-01 -1.5605E+01  0.1190E+01  4.9983E+00
> 3.0942E+00
>   2.600  5.3179E+00  5.7289E-01 -1.5987E+01  0.1239E+01  4.3905E+00
> 3.2252E+00
>   2.800  5.3348E+00  5.8762E-01 -1.6217E+01  0.1258E+01  4.1537E+00
> 3.3638E+00
>   3.000  5.3246E+00  5.9586E-01 -1.6383E+01  0.1257E+01  4.0743E+00
> 3.5096E+00
>   3.200  5.3065E+00  6.1650E-01 -1.6474E+01  0.1250E+01  4.0802E+00
> 3.6618E+00
>   3.400  5.2733E+00  6.3374E-01 -1.6567E+01  0.1239E+01  4.1398E+00
> 3.8197E+00
>   3.600  5.2309E+00  6.4470E-01 -1.6663E+01  0.1226E+01  4.2364E+00
> 3.9827E+00
>   3.800  5.1752E+00  6.3603E-01 -1.6766E+01  0.1212E+01  4.3604E+00
> 4.1501E+00
>   4.000  5.1090E+00  6.0562E-01 -1.6883E+01  0.1198E+01  4.5058E+00
> 4.3214E+00
>   4.200  5.0331E+00  5.5941E-01 -1.6984E+01  0.1183E+01  4.6683E+00
> 4.4959E+00
>   4.400  4.9489E+00  4.9872E-01 -1.7115E+01  0.1168E+01  4.8452E+00
> 4.6734E+00
>   4.600  4.8588E+00  4.2625E-01 -1.7230E+01  0.1154E+01  5.0343E+00
> 4.8533E+00
>   4.800  4.7653E+00  3.5048E-01 -1.7327E+01  0.1139E+01  5.2341E+00
> 5.0355E+00
>   5.000  4.6691E+00  2.7395E-01 -1.7453E+01  0.1125E+01  5.4434E+00
> 5.2195E+00
>   5.200  4.5722E+00  1.9793E-01 -1.7590E+01  0.1110E+01  5.6610E+00
> 5.4051E+00
>   5.400  4.4760E+00  1.3243E-01 -1.7866E+01  0.1096E+01  5.8864E+00
> 5.5922E+00
>   5.600  4.3817E+00  8.0754E-02 -1.8387E+01  0.1083E+01  6.1187E+00
> 5.7805E+00
>   5.800  4.2890E+00  7.7722E-02 -1.9408E+01  0.1070E+01  6.3576E+00
> 5.9699E+00
>   6.000  4.1996E+00  1.2225E-01 -1.9952E+01  0.1058E+01  6.6024E+00
> 6.1603E+00
>   6.500  3.9822E+00  2.6906E-01 -2.0350E+01  0.1031E+01  7.2385E+00
> 6.6398E+00
>   7.000  3.7681E+00  3.8170E-01 -2.0473E+01  0.1010E+01  7.9052E+00
> 7.1233E+00
>   7.500  3.5495E+00  4.3899E-01 -2.0529E+01  0.9919E+00  8.5988E+00
> 7.6098E+00
>   8.000  3.3245E+00  4.4840E-01 -2.0549E+01  0.9763E+00  9.3169E+00
> 8.0987E+00
>   8.500  3.1062E+00  4.3705E-01 -2.0526E+01  0.9613E+00  1.0057E+01
> 8.5893E+00
>   9.000  2.8953E+00  4.1495E-01 -2.0476E+01  0.9480E+00  1.0818E+01
> 9.0814E+00
>   9.500  2.6939E+00  3.9247E-01 -2.0391E+01  0.9367E+00  1.1598E+01
> 9.5746E+00
>  10.000  2.4999E+00  3.7170E-01 -2.0271E+01  0.9291E+00  1.2396E+01
> 1.0069E+01
>  11.000  2.1169E+00  3.6890E-01 -1.9990E+01  0.9196E+00  1.4041E+01
> 1.1059E+01
>  12.000  1.7611E+00  4.1306E-01 -1.9816E+01  0.9119E+00  1.5747E+01
> 1.2052E+01
>  13.000  1.4328E+00  4.6749E-01 -1.9744E+01  0.9072E+00  1.7507E+01
> 1.3046E+01
>  14.000  1.1169E+00  5.1022E-01 -1.9760E+01  0.9054E+00  1.9317E+01
> 1.4041E+01
>  15.000  8.2534E-01  5.3666E-01 -1.9821E+01  0.9032E+00  2.1172E+01
> 1.5037E+01
>  16.000  5.5314E-01  5.4489E-01 -1.9903E+01  0.9025E+00  2.3070E+01
> 1.6034E+01
>  17.000  2.9163E-01  5.3763E-01 -2.0012E+01  0.9015E+00  2.5007E+01
> 1.7031E+01
>  18.000  4.7223E-02  5.2008E-01 -2.0124E+01  0.8986E+00  2.6981E+01
> 1.8029E+01
>  19.000 -1.8906E-01  4.9327E-01 -2.0255E+01  0.8968E+00  2.8989E+01
> 1.9027E+01
>  20.000 -4.1335E-01  4.6035E-01 -2.0384E+01  0.8947E+00  3.1029E+01
> 2.0025E+01
>
>
>
>
>
>
>
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