The ABINIT Users Mailing List ( CLOSED )

[Xavier Gonze <gonze@pcpm.ucl.ac.be>]

Dear George,

Thanks for your investigations.
Perhaps the bug is only in the cut3d treatment of the istwfk=1 case ?

Xavier

On 03 May 2006, at 02:20, Shu Heng Pau wrote:

> Hi,
>
> I think the option istwfk = 1 is faulty.  If I insist on not using the
> time-reversal symmetry for k = [0 0 0]  (thus istwfk = 1), I  
> occasionally end
> up getting a complex wavefunction.  When I set istwfk = 2, I always  
> obtain the
> correct output --- a real wavefunction.
>
> Thus, unless the use of istwfk =1 for k=[0 0 0] is illegal, I think  
> there is a
> bug.
>
> Thanks,
> George
>
>
> Quoting Shu Heng Pau <gpau@MIT.EDU>:
>
> > Hi,
> >
> > Thank you, Matthieu.  I believe I have done all the points  
> > mentioned below and
> > am still getting a complex wavefunction:
> >
> > 1. Gamma point used: included the keyword kpt 0 0 0.
> > 2. The phase is not constant: imag(psi)/real(psi) is not constant.
> > 3. istwfk is set to 1.
> > 4. and xred is set to  -0.125 -0.125 -0.125; 0.125  0.125  0.125.
> >
> > For the cut3d, I have used option 4 and the output for the 4th psi  
> > can be found
> > here:
> >
> > http://web.mit.edu/~gpau/Public/abinit/
> >
> > In the above folder, I have also included my input files, my  
> > pseudopotential
> > file and the output file.  Note that I have excluded the nonlocal  
> > part of the
> > pseudopotential and also core correction.  I have previously done  
> > a simulation
> > for a single atom with simple cubic structure --- both the psi  
> > obtained are
> > real though.
> >
> > Is there any other reasons that may lead to a complex wavefunction?
> >
> > Thanks,
> > George
> >
> > Quoting Matthieu Verstraete <mjv500@york.ac.uk>:
> >
> > > Hi -
> > >
> > > The default behavior of abinit is to use a shift of 0.5 0.5 0.5  
> > > for the kpoints. Check the values in the kpt array of your  
> > > output. In your case this still brings you to the "zone boundary"  
> > > where the wavefunctions can still be chosen as real. The  
> > > operative word is "can": as you said yourself it can have an  
> > > arbitrary phase.
> > >
> > > In our case the psi are stocked in reciprocal space, where this  
> > > implies 1/2 the coefficients can be obtained from the other 1/2  
> > > using symmetries (k -> -k+G), but for k/=Gamma I'm not sure this  
> > > is equivalent to making the choice "psi real". So
> > >
> > > 1) make sure you really are using Gamma and not L
> > >
> > > 2) look at the value of istwfk which states how the coeffs are  
> > > stocked and recreated using symmetries. If you set istwfk to 1  
> > > and still have your problem, and are sure you're using gamma  
> > > _and_ that it's not just a phase shift, then we may have a bug...  
> > > Possibly in the way the wfk are output. You used cut3d? Which  
> > > mode, etc?
> > >
> > > 3) Oh, yeah, it may be linked to your choice of unit cell: yours  
> > > doesn't explicitly include inversion symmetry. Use
> > >
> > > xred -0.125 -0.125 -0.125
> > >       0.125  0.125  0.125
> > >
> > > to be sure. Or try a simpler system (1 atom/UC).
> > >
> > > Matthieu
> > >
> > > --
> > > ================================================================
> > > Dr. Matthieu Verstraete                 mailto:mjv500@york.ac.uk
> > > Dept. of Physics, University of York,     tel: +44 1904 43 22 08
> > > Heslington, YO10 5DD York, United Kingdom fax: +44 1904 43 22 14