The ABINIT Users Mailing List ( CLOSED )

[<6671011@163.com>]

Dear Matthieu,

While calculating the band structure (BS) of a 1D semiconductor (Eg ~0.4 eV), 
I
found the following strange behaviors:

(1) In Abinit 5.6.4 (tsmear=0)

                plot of GS-Eigenvalues --->  semiconductor,
                plot of BS-Eigenvalues --->  metal (obviously wrong).

To solve the problem, I have to use much denser kpoints in the GS.


(2) In CATSEP (included in the GUI---Materials Studio (MS)), I used the 
exactly
same kpoints and similar other parameters, but got:

                plot of GS-Eigenvalues --->  semiconductor,
                plot of BS-Eigenvalues --->  semiconductor.
 
------------------

The above difference confused me a lot. Today, after your reply, I did some
further tests and got the answer. Actually, CATEP give almost the same 
original
results as Abinit, but the MS does some extra process and causes the above
difference. The only file used by MS in Band Structures Analysis is *.bands,
which contains the following information:

                A.  Number of electrons in a cell
                B.  Fermi energy of GS
                C.  Eigenvalues

The trick used by MS is: If A and C deduce a semiconductor, then ignore B and
get a new Fermi energy according to A and C; Or else, use B and C.

-----------------


Sincerely,
Gunagfu Luo


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CASTEP should be calculating the EF in the same way. What do you mean that it
is not good enough? The non-SCF GS is a good way of getting a more precise EF,
and I would also decrease tsmear (also make sure that this is identical btw
abinit and CASTEP - it is the most influential factor).

Matthieu


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On Sat, Feb 14, 2009 at 6:46 PM, <6671011@163.com> wrote:

Dear Matthieu,

Thanks for explanation.

The problem I met is that the EF in the SCF-GS is not accurate enough for the
BS. So, according to your reply, the only reasonable solution is improving the
SCF-GS calculation?  Or maybe I could add a non-SCF GS calculation between the
SCF-GS and the BS calculation?

p.s. I am dealing with 1D system. And there is no such problem when I work 
with
CASTEP at almost the same accuracy level.


Sincerely,
Guangfu Luo


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The Fermi energy should be taken from the full GS calculation, not the BS,
whose k-points are not weighted and distributed evenly throughout the 
Brillouin
Zone. Also, there is no need to calculate the Fermi energy as the density is
already fixed. This is why EF is not output for the non scf case.

Matthieu


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On Sat, Feb 14, 2009 at 1:31 AM, <6671011@163.com> wrote:

Dear Friends,

  I hope to obtain the Fermi Energy in the Band Structure calculation.
However, Abinit does not export it in the default situation, though it does
that in the GS calculation.

 Is it possible to get it easily by setting some parameter? (I can get the
Fermi Energy according to its definition in the Band Structure, but probably
Abinit has this function already.)


Thanks a lot.

Sincerely,
Guangfu Luo