The ABINIT Users Mailing List ( CLOSED )

[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