[Ifeffit] charge transfer by SCF in FEFF8 and simulation for charge disproportionation

[Ying Zou]

Dear all,

I am doing a SCF calculation by Feff8.40 for a model compound
PbTiO3. However, the obtained charge transfer deviates far away from
its well-known formal oxidation state. According to common electron 
negativity data, the oxidation state would be:

Pb  2+
Ti  4+ 
O   2-

The SCF run gave out charge transfer for those atoms as following:

Pb 0.717
Ti 0.181
O  -0.300

After I read through the existing threads on charge transfer in this list, I know that transfered charge FEFF gives out is just a portion of general formal oxidation state. Can we undderstand that this is just ionic portion for entire bonding? Such as for oxygen, "-0.300" is ionic bonding, while the rest of valency (-1.700) exists as covalent bonding, which doesn't have apparent charge transfer by definition. 

Another related question is then: is there any way in FEFF to take into account this "covalence" part? (maybe deriving from overlapping area of mufftin-potential?) I think this may be crucial for a self-consistent analysis of charge disproportionation. 

Any comments on this would be greatly appreciated. Attached please see"atom.inp" and "feff.inp". Thanks so much!


Ying


Ying Zou
Research associate,Dr. Phys.
Physics Department, UWM


***************atoms.inp***********************************
! This atoms input file was generated by WebAtoms 1.8 (Atoms 3.0beta10)
! Atoms written by and copyright (c) Bruce Ravel, 1998-2001
title = Perovskite: PbTiO3
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	rmax =	  4.2950
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

******************************************************************



************feff.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
*******************************************************************