The ABINIT Users Mailing List ( CLOSED )

[<rolando.saniz@ua.ac.be>]

Dear all,

We are trying to calculate the formation energy of some doped semiconductors.
We are interested, in particular, in the case in which the dopant is in a
charged state. But we are uncertain about a few points:

(i) In the charged state, one adds (or removes) an electron from the system,
and a uniform compensating background charge is then added to the system. The
question is if the total energy is correctly given by Abinit also in that 
case.
This is important, because it is the first term in a relatively complicated
expression giving the formation energy of charged impurities [see, e.g., van 
de
Walle & Neugebauer, J. Appl. Phys. 95, 3851 (2004)].

(ii) In the charged state, the system often is metallic. In that case one has
to use an occopt parameter value appropriate for metals and a non-zero value 
of
tsmear. The problem we ran into is that the total energy depends on the value
of tsmear, affecting the final formation energy value in a non-negligible way.
Which tsmear gives the correct formation energy? Would the smallest tsmear
value be the best? (is it possible to use tsmear=0?). Note that the undoped
system is an insulator, so does not require tsmear. So one ends up comparing a
total energy that is calculated with no tsmear, and one with a finite value of
tsmear, which we find problematic.

(iii) When one uses a finit value of tsmear, the total energy in the output
file has an additonal term proportional to kT. What's the meaning of this 
term,
considering that, in principle, tsmear is introduced for technical reasons and
does not necessarily represent a temperature smearing?

We look forward to comments on the above.

Best regards,
R. Saniz