### how to get the irreducible q-points for phonon calculations

Posted:

**Wed Jul 28, 2010 5:19 pm**When doing a phonon calculation, only the irreducible perturbations need to be calculated, and abinit and anaddb will complete them by symmetry. In particular, the dynamical matrix will be completed and symmetrized at each q-point.

To get the irreducible q-points for your system, you can do a small auxiliary calculation (with low ecut and minimal bands). Make a new directory, and copy your input file for the ground state there. If you set the k-point grid (

From the header of the log or output file, the <b>kpt</b> points can be copied directly to the phonon input file, as q-points.

To get the irreducible q-points for your system, you can do a small auxiliary calculation (with low ecut and minimal bands). Make a new directory, and copy your input file for the ground state there. If you set the k-point grid (

**ngkpt**) to be equal to the q-point grid you want for the phonons, and set**kptopt**to 1. Also, don't forget to set <b>shiftk</b> to 0 0 0, in order to get a non-shifted grid with the Gamma point.From the header of the log or output file, the <b>kpt</b> points can be copied directly to the phonon input file, as q-points.