[Wien] total energy of indevudual atom for cohesion energy

[L. D. Marks]

Someone else might have a solutions, but I think you have run into one of 
the cases where DFT does not really get the right answer (at least at the 
moment). The ground state of the atom is 3d24s2 with a spin of two, but 
DFT will give it a state closer to 3d34s1 (or even 3d4). An empirical 
observation is that the better your Hamiltonian is (and you can only 
control GMAX, RKMAX, RMT for this) the better Wien2k and probably other 
DFTs converge. Because the Hamiltonian for Ti is not really right, it does 
not want to converge and you have to use a VERY small mixing (0.01) some 
smearing (I suggest TEMP of around 0.001) and some careful checking (don't 
just let it run and assume it is OK!). Fe may be better, I've never tried.

You are not going to get the number for Ti really right by DFT. I've seen 
some papers where people calculate an excited state and "correct it" with 
experimental values but I don't think this is correct.

On Tue, 13 Jun 2006, youcef bouhadda wrote:

> Dear Wien-users,
> to calculate the cohesion energy (enthalpy also) I try
> to  calculat the total energy of indvedual atom, so i
> have seen the FAQ and also the mailling list and i
> have do this:
> for FeTi (exemple) its seems ok for the system, and
> when i do the calculation for the induvidual atoms
> (Ti, Fe), i have increase the parametre lattices
> (25.0bohr) in the FCC system with the same RMt and
> Rkmax of the FeTi calculation:
> first, the Scf cycle give this message
> *excuting run-lapw -cc 0.0001
> *return key to continue
> so i have decrease the Gmax and the SCF cycle start
> and after 20 iterations i have no convergence !! i
> have try to change the factor in case.inm but nothing!
> Any suggestions?
> and i have an other question: why we choose the FCC
> structure ? (can we choose other structur?)
> Thanks in advance
>
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-----------------------------------------------
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2225 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
http://www.numis.northwestern.edu
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