[QE-users] What's representation 0 in ph.x?

[ykhuang]

I'm sorry for attaching Luiz's mail by mistake. I rewrite my mail. Really sorry. Hi, QE users.Recently I plan to perform free energy calculations of CO absorption using ph.x, matdyn.x, q2r.x and fqha.x. However, I meet mainly 2 problems.1. When I do phonon calculation of isolated CO molecule with q points sampling automatically 2x2x2, I find large negative frequency emerges in DOS. Could anyone tell me why ph.x yields negative frequency? Moreover if I want to eliminate the negative frequency, should I decrease the tr2_ph value?2. When I do phonon calculation of the CO absorbed slab, to simplify the calculation, I set start_irr and last_irr parameters including three translational degrees of freedom of C and O atom. However, after each q point iteration, ph.x outputs one line like:Not Davison diagonalization, representation 0 is not done.As a result, no frequency information is yielded, although ph.x job terminates normally. However, it is hard to understand representation 0, because irreducible representation in ph.x is marked from 1, not 0. I don't know how I can solve this problem.Any suggestions will be appreciated. Best regards.Yike HuangPhD candidate.Dalian Institute of chemistry and physics, CAS, China.
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