GGA tag

Message

alexabr · #1 Post by **alexabr** » Tue Aug 21, 2007 9:33 am

Hello VASP users,

I tried to utilize GGA tag in my calculations and I got warnings using value GGA = RP with potpaw_PBE pseudopotentials:

---
You enforced a specific xc-type in the INCAR file,
a different type was found on the POTCAR file
---

But calculations proceeded. This warning does not appear in case of GGA = PE which is natural as LEXCH = PE in POTCAR. I hope this is just information warning. Moreover GGA = PE works even with potpaw_GGA pseudopotentials but with the same warning. I suspect that the results of calculations will be meaningless in the latter case.

For potpaw_GGA pseudopotentials GGA = 91 (VOSKOWN = 1) works perfectly. But GGA = PB, PW, and LM cause the same warning and error message for these pseudopotentials (potpaw_GGA):

---
internal ERROR GGAEALL: Wrong LEXCHG, scheme not implemented!
---

Calculations are failed to proceed. I tried to use other pseudopotentials (pot, pot_GGA, potpaw, potpaw_PBE) but I got the same error in case of GGA = PB, PW, and LM.

My question is which pseudopotentials should be used with GGA = PB, PW, and LM?

Many thanks in advance.

Perhaps this is physical question. Is there any opportunity to remove it from the bugs section...
<span class='smallblacktext'>[ Edited ]</span>

#2 Post by **admin** » Wed Aug 22, 2007 12:36 pm

1) this is just a warning to verify that you have modified LEXCH by setting the GGA tag in INCAR different from POTCAR explicitely
2) the Vosko-Wilk-Nusair formalism only needs to be used for the parametrization of the XC- contribution of the free electron gas if the PW91 parametrization is used.
3) if the GGA tag is set in INCAR, the XC is calculated accordingly, irrespective of the XC-type defined by POTCAR. --> you can take any POTCAR

alexabr · #3 Post by **alexabr** » Wed Aug 22, 2007 1:05 pm

Thank you.
VOSKOWN = 1 was set only for GGA = 91
Other cases (GGA = PB, PW, and LM) used default VOSKOWN.

alexabr · #4 Post by **alexabr** » Thu Aug 23, 2007 2:19 pm

Might it be a version dependent issue? I use VASP 4.6.

alexabr · #5 Post by **alexabr** » Sat Aug 25, 2007 3:43 pm

For the GGAALL subroutine I found this comment string in the xcgrad.f source file

---
! presently only PW91, PBE and RPBE are implemented
---

Indeed the GGAALL subroutine recognises only three types of the GGA functionals LEXCHG = 4, 5, and 6 (Perdew-Wang 91, Perdew-Burke-Ernzerhof, and revised Perdew-Burke-Ernzerhof respectively). It is written in the comments that for the other functionals finite differences are used. But in the ELSE branch responsible for the other functionals there is invoke of the GGAEALL subroutine doing the only job of printing the error message 'internal ERROR GGAEALL: Wrong LEXCHG, scheme not implemented!' and stopping the calculations.

Does it mean that GGAEALL gradient correction routine is not implemented yet and there is no hope to perform calculations with Perdew-Becke, Perdew-Wang 86, and Langreth-Mehl-Hu GGA functionals without coding this routine?

zhzeng · #6 Post by **zhzeng** » Mon Jul 21, 2008 1:10 pm

RP of GGA tag is a liitle ambiguous. I think it is good if the administrator can give a definite statement.
I.E. It is for
revPBE of Y. Zhang and W. Yang, Phys. Rev. Lett. 80, 890 (1998)
or
RPBE of B. Hammer, L.B. Hansen and J.K. Norskov, Phys. Rev. B 59, 7413 (1999)

Thanks!

egillsk · #7 Post by **egillsk** » Fri Feb 24, 2012 5:08 pm

has this question by Zhenhua never been answered here at the forum?

We just got an accepted paper where the referee points out to us that he or she has been informed by the vasp admins that RP is really the RPBE by Hammer et al, but not the revPBE by Zhang and Yang, as indegated in the manual.

Our paper is soon going in the Press and we would like to have this cleared up asap, so we can change this if needed in the paper.

thanks,
egillsk

#8 Post by **admin** » Mon Feb 27, 2012 1:13 pm

RP uses parametrization according to B. Hammer, L.B. Hansen and J.K. Norskov, Phys. Rev. B 59, 7413 (1999)