[Wien] Wien vs. FEFF

[Jorissen Kevin]

Dear Pedro,
 
that's a rather general question ...
 
Feff is a real-space method, essentially meant for 'clusters' of atoms (which may well represent an infinite solid), while wien is a reciprocal space ('band structure') method, meant for periodic solids (which may, using supercells, represent finite structures in a way).
While feff uses Green's functions to propagate electrons around the cluster, wien calculates eigenstates by diagonalizing a hamiltonian, and then (in the telnes program) calculates transition probabilities between states for the spectrum.
 
So the theories definitely have differences.  Is that what you mean by 'complementary'?
There are also a lot of effects which neither of the programs get right : wien is ground-state, and feff (currently) only has one-electron Green's functions; that's not good enough to treat excited states accurately (think of core hole effects, etc.)
 
I would encourage you to read the papers which describe the two methods; there's a PRB by M. Nelhiebel, C. Hébert, ... describing telnes and wien; and there's another PRB by A. Ankudinov, J. Rehr, ... describing the feff program rather well; you should find the precise references in the manuals, or ask me for them (I'm not at my office right now).
Also, both codes have example cases which you can run.
 
I have experience with both methods, and like both rather well.  For excitation spectra, both will often serve will and will also let you down in other occasions.  I cannot make general statements like 'for those materials, or for those edges you should use this method, and not the other'.
 
Bear in mind that feff calculates XANES (x-rays, not electrons).  Though this is theoretically very similar to elnes, there are small differences (basically, a factor energy loss in the cross section).  The input for wien's telnes program may also be a little more convenient if you are used to electrons.
 
Speaking very generally, I would say that wien, as an electronic structure code, has definitely the most features (many material properties can be calculated, and you have a lot of control).  On the other hand, this makes wien a lot more difficult to use than feff.
If you want results fast, or if you are not planning to spend a lot of time in getting to know a code, feff may be a better choice.  It is a very user friendly code : no worries about compilation, a single input file describing all of the calculation.
 
 
 
 
Kevin Jorissen
 
EMAT - Electron Microscopy for Materials Science   (http://webhost.ua.ac.be/emat/)
Dept. of Physics
 
UA - Universiteit Antwerpen
Groenenborgerlaan 171
B-2020 Antwerpen
Belgium
 
tel  +32 3 2653249
fax + 32 3 2653257
e-mail kevin.jorissen at ua.ac.be
 

________________________________

Van: wien-admin at zeus.theochem.tuwien.ac.at namens Pedro Costa
Verzonden: vr 7-1-2005 12:57
Aan: wien at zeus.theochem.tuwien.ac.at
Onderwerp: [Wien] Wien vs. FEFF


Dear users list,
 
Could someone explain me the main differences between the Wien and FEFF programmes?
 
Are these softwares complementary for ab initio calculations of electronic structure and spectroscopic properties of materials (I am specifically interested in theory of EELS)?
 
Thanks,
 
Pedro
 
Pedro MFJ Costa
Department of Materials Science and Metallurgy
Pembroke Street, Cambridge, CB2 3QZ
 
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