Effect of time-reversal symmetry on SCF convergence

Running Abinit Ground state
1

Hello all,

I am trying to calculate the positron annihilation momentum distribution spectrum produced by a vacancy. The input file in the tutorial uses istwfk *1. After trying this, I found that this parameter severely affects the convergence of the SCF cycle. With all other parameters exactly the same, using the default value of istwfk can complete the GS calculation within no more than 100 SCF cycles, but using istwfk *1 causes the total energy obtained from each SCF cycle to fluctuate dramatically, with no sign of convergence at all.

Is this normal? Do I need to use a higher ecut and nkpt to compensate for this?

And, what is the purpose of using istwfk *1 to deactivate time-reversal symmetry in the above tutorial? If it is to get a uniform k-point grid in the momentum space, is that parameter still important if I only use the gamma point?

Thanks!

2

Dear iavas,
The divergence of the SCF can happen when you remove symmetries. This can be improved by reducing the diemix, diemixmag or increasing the nline flags.
I do not not to which extend the istwfk=1 is important for the positron calculation but what about if you run the istwfk=1 calculation by reading the WFK or DEN file of the converged case with the default istwfk?
Best wishes,
Eric