By looking at the FEFF.inp file it appears that the path in question is a Ti-O-Ti where the angle of this linkage is very close to 180 degree (had it been 180 degree, the total length would be not 3.9317 but either 3.90500 or 4.15600. In a perovskite with Ti on center such angle would be 180 degree but in your input file you have TiO6 octahedron displaced relative to the Pb corners in 100 direction (also known as tetragonal distortion). Still, the angle is close to 180 degree which makes a contribution of forward scattering, triple-scattering paths that go through O in forward direction twice, the strongest - and that should explain why your path amplitude increased over 100 percent. Why the two programs give different amplitude, must be a bug, as Bruce and Scott explained. Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@millenia.cars.aps.anl.gov]On Behalf Of Ying Zou Sent: Thursday, August 28, 2008 6:42 PM To: ifeffit Subject: Re: [Ifeffit] Comparison of "amp" between Feff8.40 and feff6 - Curved waves or Plane waves? Dear all, While I am calculating FEFF path through Feff8.40 using the "feff8.inp" as attached, I notice that the value of "amp" shown on "FEFF interpretation page" for some paths goes over 100%. For example, path 14 has a Reff=3.9317 far away from first shell, yet it has an "amp"=169.913. On the contrary, if I do the same in Artemis through embedded Feff6.0(using "feff6.inp"), none of paths has an "amp" over 100%. I am guessing this could be all right because Feff8 is using curved waves Feff6 instead plane waves. Any comments on this would be greatly appreciated! Ying Ying Zou Research Assoc., Dr.Phys. Physics Department, UWM =======================feff8.inp======================================= * This feff.inp file generated by ATOMS, version 2.50 * ATOMS written by and copyright (c) Bruce Ravel, 1992-1999 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * * total mu = 5194.4 cm^-1, delta mu = 761.6 cm^-1 * specific gravity = 7.942, cluster contains 25 atoms. * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * * mcmaster corrections: 0.00093 ang^2 and 0.165E-05 ang^4 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * TITLE Perovskite: PbTiO3 EDGE K S02 1.0 * pot xsph fms paths genfmt ff2chi CONTROL 1 1 1 1 1 1 PRINT 1 0 0 0 0 3 * r_scf [ l_scf n_scf ca ] SCF 3.88586 0 15 0.1 * ixc [ Vr Vi ] EXCHANGE 0 0 0 EXAFS RPATH 7.77172 * kmax [ delta_k delta_e ] *XANES 4.0 0.07 0.5 * r_fms [ l_fms ] *FMS 3.88586 ******** * *RPATH 0.10000 * emin emax resolution *LDOS -20 20 0.1 POTENTIALS * ipot z [ label l_scmt l_fms stoichiometry ] 0 22 Ti -1 -1 0 1 8 O -1 -1 3 2 82 Pb -1 -1 1 3 22 Ti -1 -1 1 ATOMS 0.00000 0.00000 0.00000 0 Ti 0.00000 0.00000 0.00000 -1.76630 1 Oapical 1.76630 1.95250 0.00000 0.32417 1 Oplanar 1.97923 0.00000 -1.95250 0.32417 1 Oplanar 1.97923 -1.95250 0.00000 0.32417 1 Oplanar 1.97923 0.00000 1.95250 0.32417 1 Oplanar 1.97923 0.00000 0.00000 2.38970 1 Oapical 2.38970 -1.95250 -1.95250 1.91592 2 Pb 3.36084 1.95250 -1.95250 1.91592 2 Pb 3.36084 -1.95250 1.95250 1.91592 2 Pb 3.36084 1.95250 1.95250 1.91592 2 Pb 3.36084 1.95250 -1.95250 -2.24008 2 Pb 3.55563 -1.95250 1.95250 -2.24008 2 Pb 3.55563 -1.95250 -1.95250 -2.24008 2 Pb 3.55563 1.95250 1.95250 -2.24008 2 Pb 3.55563 -3.90500 0.00000 0.00000 3 Ti 3.90500 0.00000 3.90500 0.00000 3 Ti 3.90500 3.90500 0.00000 0.00000 3 Ti 3.90500 0.00000 -3.90500 0.00000 3 Ti 3.90500 0.00000 0.00000 4.15600 3 Ti 4.15600 0.00000 0.00000 -4.15600 3 Ti 4.15600 3.90500 0.00000 -1.76630 1 Oapical 4.28589 0.00000 -3.90500 -1.76630 1 Oapical 4.28589 -3.90500 0.00000 -1.76630 1 Oapical 4.28589 0.00000 3.90500 -1.76630 1 Oapical 4.28589 END ============================================================================ ========================feff6.inp========================================== * This feff6 input file was generated by Artemis 0.8.011 * Atoms written by and copyright (c) Bruce Ravel, 1998-2001 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * * total mu*x=1: 2.06 microns, unit edge step: 13.38 microns * specific gravity = 7.942 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * * Normalization correction: 0.00048 ang^2 * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * -- * * ----------------------------------------------------------------- * The following crystallographic data were used: * * title Pb Ti O3 * title Glazer A M * title # Powder profile refinement of lead zirconate titanate at several temperatures. * title # II. Pure PbTiO3 * title # Locality: synthetic * title # Sample: T = 25 C * space = P 4 m m * a = 3.9050 b = 3.9050 c = 4.1560 * alpha = 90.0 beta = 90.0 gamma = 90.0 * core = Ti edge = K * atoms * ! elem x y z tag occ * Pb 0.00000 0.00000 0.00000 Pb 1.00000 * Ti 0.50000 0.50000 0.53900 Ti 1.00000 * O 0.50000 0.50000 0.11400 Oapical 1.00000 * O 0.50000 0.00000 0.61700 Oplanar 1.00000 * ----------------------------------------------------------------- TITLE Pb Ti O3 TITLE Glazer A M TITLE # Powder profile refinement of lead zirconate titanate at several temperatures. TITLE # II. Pure PbTiO3 TITLE # Locality: synthetic TITLE # Sample: T = 25 C HOLE 1 1.0 * Ti K edge (4966.0 eV), second number is S0^2 * mphase,mpath,mfeff,mchi CONTROL 1 1 1 1 PRINT 1 0 0 0 RMAX 4.29550 *CRITERIA curved plane *DEBYE temp debye-temp NLEG 4 POTENTIALS * ipot Z element 0 22 Ti 1 82 Pb 2 22 Ti 3 8 O ATOMS * this list contains 25 atoms * x y z ipot tag distance 0.00000 0.00000 0.00000 0 Ti 0.00000 0.00000 0.00000 -1.76630 3 Oapical_1 1.76630 1.95250 0.00000 0.32417 3 Oplanar_1 1.97923 -1.95250 0.00000 0.32417 3 Oplanar_1 1.97923 0.00000 1.95250 0.32417 3 Oplanar_1 1.97923 0.00000 -1.95250 0.32417 3 Oplanar_1 1.97923 0.00000 0.00000 2.38970 3 Oapical_2 2.38970 1.95250 1.95250 1.91592 1 Pb_1 3.36084 -1.95250 1.95250 1.91592 1 Pb_1 3.36084 1.95250 -1.95250 1.91592 1 Pb_1 3.36084 -1.95250 -1.95250 1.91592 1 Pb_1 3.36084 1.95250 1.95250 -2.24008 1 Pb_2 3.55563 -1.95250 1.95250 -2.24008 1 Pb_2 3.55563 1.95250 -1.95250 -2.24008 1 Pb_2 3.55563 -1.95250 -1.95250 -2.24008 1 Pb_2 3.55563 3.90500 0.00000 0.00000 2 Ti_1 3.90500 -3.90500 0.00000 0.00000 2 Ti_1 3.90500 0.00000 3.90500 0.00000 2 Ti_1 3.90500 0.00000 -3.90500 0.00000 2 Ti_1 3.90500 0.00000 0.00000 4.15600 2 Ti_2 4.15600 0.00000 0.00000 -4.15600 2 Ti_2 4.15600 3.90500 0.00000 -1.76630 3 Oapical_3 4.28589 -3.90500 0.00000 -1.76630 3 Oapical_3 4.28589 0.00000 3.90500 -1.76630 3 Oapical_3 4.28589 0.00000 -3.90500 -1.76630 3 Oapical_3 4.28589 END ======================================================================== _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit