Looking for zero frequencies

[An Ghysels]

Dear Hutter,

Indeed, I noticed the same effect, i.e. that typically the
translational modes are well decoupled. However, I saw this effect
mainly for gas molecules. For this periodic structure, I do not agree
that the frequencies change little: eg the values -0.14095 and 0.50894
(projected) are largely influenced by the projection:
=====
Same snippet as before:
 VIB| Cartesian Low frequencies ----0.44072    -0.10876E-01
0.12458     0.69806
 VIB| Cartesian Low frequencies --- 0.71490      1.4715
2.0898      3.8120
 VIB| Cartesian Low frequencies ---  5.8007
 VIB| Frequencies after removal of the rotations and translations
 VIB| Internal  Low frequencies ----0.14095     0.50894
1.4072      2.0559
 VIB| Internal  Low frequencies ---  3.6794      5.7900
25.027      25.504
=====
So for this simple diamond case the translational modes are not
decoupled. What do you think?

On the other hand, I wonder what XC grid settings you suggest and, in
your experience, to what order of magnitude one can decrease the
zeros?

An