[Pw_forum] Problems with Polarization calculations

Paolo Giannozzi giannozz at nest.sns.it
Fri Oct 19 10:24:18 CEST 2007

On Oct 19, 2007, at 5:01 , Sohrab Ismail-Beigi wrote:

>       from  ylm_q : error # 181312304
>        not programmed for L>

> OK, that is a bit cryptic.

it depends for whom :-) It means that spherical harmonics for N > M,
M=what is printed, are not programmed. Actually Nmax =(Lmax+1)**2
because spherical harmonics are calculated and stored with a
combined index (l,m), running from 1 to (Lmax+1)**2 . This is done
consistently everywhere, even if sometimes it is not reflected in the
name of variables (for instance, "lmax" in PW/bp_ylm_q.f is misleading).

Spherical harmonics used in the Berry phase calculation are
implemented only up to L=4 (i.e. projectors up to l=2): see
PW/bp_ylm_q.f, unlike those used in the rest of the code
(see flib/ylmr2.f90) that work for any L. It shouldn't be difficult
to use the same spherical harmonics everywhere, though.

The message would have been less cryptic if N was a sensible
number (like 49=(2*3+1)**2...) instead of a funny number. The
likely reason is that something is going out of bounds BEFORE
the check in ylm_q is performed. This is obviously a bug. You can
verify this by compiling with bound check enabled (-g -C on most
compilers, -g -fbounds-check on gfortran).

> Apparently no elements with f projectors (e.g. transition metals)
> were ever used for Berry phase...!??!

apparently not. I would try to avoid f projectors in transition metals:
they are a mess even without them.

> Therefore, does the bp_c_phase.f90 code implicitly assume ultra-soft
> psps?

coming from David Vanderbilt's group, I guess so! Norm-conserving
pseudopotentials in the separable form are a special case of ultrasoft
pseudopotentials, so if it works for the latter, it works for the former
as well.

Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

More information about the users mailing list