start_irr = 235
last_irr = 240
Hello,
I did not understant that the molecule was adsorbed on a surface! In
this case it makes sense to compute several q-points (not orthogonal to
the surface!) However, if you set start_irr and last_irr, you are only
computing a few rows of the dynamical matrix. As the phonons are the
square roots of the eigenvalues of this matrix, you need the entire
matrix in order to compute them.
You can compute differents irreducible representations (irr) separately
and then combine the results together as explained in the Grid_example
of phonon. But you still need all the matrix. If you have reason to
think that the CO vibration is completely decoupled from the rest of the
system, you may try to get its vibrational frequency by doing finite
differences. It would also be possible to modify phonon to only compute
the minor of the dynamical matrix that involve CO, then diagonalize it,
but it is not currently implemented.
hth
--
Lorenzo Paulatto - Paris
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