Re: [Wien] Fwd: Likely source/s of stupid kgen error

There is no problem with kgen.

Your two structures are P  and B lattices.

You will never be able to make identical k-meshes for them, as the BZ is different and also the size of the unit cell and number of atoms/unit cell differ by a factor of 2 (although one specifies the same lattice parameters a,b,c).

It is like: bcc Fe and Fe in a simple cubic cell with 2 atoms/cube.

For a comparison of fine details one has either to converge both k-meshes, or double the cell (making the B cell --> P), then constraining symmetry by labelling some atoms). Then the k-meshes can be made identical.

Am 07.09.2016 um 16:11 schrieb Laurence Marks:
One of my students noticed an inconsistency in basdiv.f which might be
a source of a problem she has (or not), see below. For certain the
code and comments appear to be inconsistent:

if((iarb(1).eq.1).and.(n(1).ne.n(2))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and y direction'
goto 123
endif
if((iarb(2).eq.1).and.(n(1).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and z direction'
goto 123
endif
if((iarb(3).eq.1).and.(n(1).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in y
and z direction'
goto 123
endif
endif

Suggestions?

---------- Forwarded message ----------
From: Tassie Andersen <tasskand...@gmail.com>
Date: Tue, Sep 6, 2016 at 12:21 PM
Subject: Likely source/s of stupid kgen error
To: Laurence Marks <l-ma...@northwestern.edu>

Hello Laurie,

I think I may have found the source/s of the kgen error I described. I
searched for the exact error message in \$WIENROOT/SRC_kgen and found
something helpful in basdiv.f . From what I can tell this file takes
in some variables, one of which describes whether the unit cell has
any equal length dimensions (x ,y , z), this is described in the
heading info by 'IARB' .

The problem is that later, when it checks the values of IARB (and can
generate a subsequent error message) it uses the following routine
with cases to check against :

if(NMSHP.le.0) then
123    write(*,*) " Specify 3 mesh-divisions (n1,n2,n3):"
if((iarb(1).eq.1).and.(n(1).ne.n(2))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and y direction'
goto 123
endif
if((iarb(2).eq.1).and.(n(1).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and z direction'
goto 123
endif
if((iarb(3).eq.1).and.(n(1).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in y
and z direction'
goto 123
endif
endif
NMSHP=(N(1)+1)*(N(2)+1)*(N(3)+1)
RETURN
END

Notice that case 'if((iarb(2).eq.1).and.(n(1).ne.n(3))) then' and
'if((iarb(3).eq.1).and.(n(1).ne.n(3))) then' have the same
requirements for variable n. This should probably be the following

if(NMSHP.le.0) then
123    write(*,*) " Specify 3 mesh-divisions (n1,n2,n3):"
if((iarb(1).eq.1).and.(n(1).ne.n(2))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and y direction'
goto 123
endif
if((iarb(2).eq.1).and.(n(2).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in x
and z direction'
goto 123
endif
if((iarb(3).eq.1).and.(n(1).ne.n(3))) then
write(*,*) 'Lattice symmetry requires equal mesh in y
and z direction'
goto 123
endif
endif
NMSHP=(N(1)+1)*(N(2)+1)*(N(3)+1)
RETURN
END

However, in the intro commented text there's a note saying '2 and 3
are reversed?' so I'm not sure is IARB(2)=1 specifies if y = z or if x
= z (vice versa with IARB(3) = 1). So either the fix I propose or the
corresponding one for the iarb(3) condition needs to be altered.
However, this doesn't solve the root of the problem (though it is
annoying and keeps you from entering the proper values).

The real issue is that my structure, where x=y=/=z should have
iarb(1)=1 and iarb(2), iarb(3) =/= 1. Somehow iarb(2) is being set to
1 in this particular case (but not others with a different symmetry
group). The only file I can find that sets IARB values is bravai.f (or
birken.f or bravai_bla, but these two don't seem to be called ever). I
can't figure out where it's messing it up though. It'd be good to
print all three IARB values after bravai.f runs to check it but I'm
not sure how to do that. Any suggestions are appreciated.

So it seems there are at least 2 issues.

Regards,
Tassie

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