The ABINIT Users Mailing List ( CLOSED )

[Gian-Marco Rignanese <rignanese@pcpm.ucl.ac.be>]

Dear All,

Some of you have recently reported a problem with the GW calculations 
in ABINIT. We have tracked the origin of this problem to the presence 
of non-symmorphic operations in the symmetries list after suppressing 
those related through the inversion symmetry. The possibility to deal 
with this kind of operations is not yet included in the GW part of 
ABINIT (we hope that it will be in a "near" future).

So far, the program would just give a WARNING ("The GW program may give 
incorrect results"). Starting from ABINITv3.4.3, we have decided to 
replace this WARNING by an ERROR. Therefore, the program will not 
produce the _KSS file when non-symmorphic operations in the symmetries 
list after suppressing those related through the inversion symmetry.

What should be done to go further in such situations?

1) In some simple cases, it is possible to choose the atomic positions 
in such a way to get rid of the problem. For instance, in the case of 
Silicon (2 atoms unit cell), one can choose either:
xred       0.000  0.000  0.000          0.250  0.250  0.250
or:
xred     -0.125 -0.125 -0.125          0.125  0.125  0.125

In the first case, the GW calculation works perfectly; while in the 
second one, the rotations (without inversion) are non-symmorphic.

2) In the other cases, the symmetries list should be checked in 
details. All the symmetries that are related through the inversion are 
now (from ABINITv3.4.3 on) indicated explicitly in the log file. The 
remaining operations that are non-symmorphic can thus be found easily. 
Finally, the calculation should be restarted with the list of 
symmetries that should be taken into account explicitly indicated in 
the input file (use nsym, symrel and tnons).

Best regards,

Gian-Marco.