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[<michel.cote@umontreal.ca>]

Hello Paul,

I have experience with Abinit and with Paratec since I am a former member of 
the Steven and Cohen group at Berkeley. I have also experience with the GaAs 
semiconductor.

Here what I found for the GaAs system:

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

When we use the TM pseudopotentials of the Abinit web page for Ga and
As (31ga.pspnc, 33as.pspnc), we had a large error in the lattice
parameter (opt at 10.29726 a.u. compare with exp at 10.677 (Kittel),
3.6% error). I then notice that these peudo did not have a d
component. I generated new pseudopotentials with the code fhi98pp
including the d component (pseudo 31-Ga:tm.fhi and 33-As:tm.fhi). I
had some problems (ghost state) when I use the local d for ga so i put
both local at p. This improved the lattice to about 10.45. I then
included partial core charge for the Ga (31-Ga:tm_with_core.fhi). With
this pseudo and 33-As:tm.fhi for the As, the optizimed lattice is
10.56888 a.u. so the error now is 1.01% which is acceptable.
 
--------------------

Now, an error of 1 or 2 mRyd between the code is very good! Especially if the 
pseudopotentials were gerenated with different codes. There are many ways to 
fit the core charge and this can made the difference between the two codes. I 
seem to recall that the atom code use in Berkeley uses a different procedure 
than the FHI code.

Michel

*************************************************************** 
  Michel Cote                          tel: +1 (514) 343-5628     
  Professeur adjoint                   fax: +1 (514) 343-2071               
  Département de physique
  Université de Montréal
  C.P. 6128, succ. Centre-ville
  Montréal (Québec) H3C 3J7          Michel.Cote@umontreal.ca
  Canada              http://carbone.pmc.umontreal.ca/~michel
***************************************************************
  
  
                          



> -----Message d'origine-----
> De : Paul Tangney [mailto:tangney@civet.berkeley.edu]
> Envoyé : 27 mars, 2003 04:17
> À : forum@abinit.org
> Objet : [abinit-forum] Nonlinear-core corrections
> 
> 
> Dear ABINITioners,
> 
> Has anybody encountered problems with nonlinear core corrections
> in ABINIT ?
> 
> I am using pseudopotentials that I generated with the Fritz-Haber
> code FHI98PP. The total energy that I get disagrees slightly with
> the results using the PARATEC plane wave code. Differences are of
> the order of 1 or 2 mRyd. (and about 4 GPa in the stress).
> The system is GaAs - I haven't checked other systems, but if
> I make PPs without core-corrections I can get both codes to agree to a
> high precision.
> 
> I am a new user of ABINIT (and also PARATEC) and so the problem
> might be something very simple, but before I get my hands dirty
> by delving into the source I thought I should ask to try to
> figure out whether the problem is with me, PARATEC, or ABINIT.
> In particular, I'm a little confused about the input variables
> "rchrg","fchrg" and "qchrg" that are on the 4th line of the
> PP files. I have set rchrg to 10.0 where the core charge is zero
> and I have values of 1.0 for both fchrg and qchrg but I don't
> know if this is correct.
> 
> I would be very grateful for any help you could give me.
> 
> Best regards,
> 
> 
> Paul
> 
> 
> 
> -- 
> Paul Tangney
> OoOo-------------------------------------------------------------
> University of California at Berkeley   /    Phone : (510) 642-2635
> Physics Department #7300       /       Home Phone : (510) 883-1259
> 366 Le Conte Hall             /               Fax : (510) 643-9473
> Berkeley, CA 94720       /      Email : tangney@civet.berkeley.edu
> Home page : http://civet.berkeley.edu/tangney/
> -----------------------------------------------------------------
> 
> 
>