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

[ykhuang]

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.
-------- 原始信息 --------发件人： Luiz Gustavo Davanse da Silveira <lgsilveira at fisica.ufpr.br> 日期: 2020/2/19  21:03  (GMT+08:00) 收件人： users at lists.quantum-espresso.org 主题： [QE-users] Advices on ralaxing perovskite supercells Greetings,I am using QE 6.4.1 to relax the atomic positions of a BiFeO3 40 atomsupercell, but the calculation didn't converge after 100 scf steps (thefinal scf accuracy was about 5E-4). I am a new QE user and I really don'tknow what to change in order to the calculation successfully run. Anyadvice is very much appreciated.My input follows bellow:&control	calculation = 'relax'	prefix = 'bfo'	pseudo_dir = './sssp'	outdir = './outdir'	etot_conv_thr = 1.0e-5	forc_conv_thr = 1.0e-4/&system	ibrav = 0	nat = 40, ntyp = 3,	ecutwfc = 120, ecutrho = 960	lda_plus_u = .TRUE., Hubbard_U(2) = 4/&electrons	conv_thr = 1e-6/&ions	ion_dynamics = 'bfgs'/ATOMIC_SPECIES Bi 208.98 Bi_pbe_v1.uspp.F.UPF Fe 55.85 Fe.pbe-spn-kjpaw_psl.0.2.1.UPF O 16 O.pbe-n-kjpaw_psl.0.1.UPFATOMIC_POSITIONS (crystal) Bi 0.000000000000000     0.000000000000000     0.000000000000000 Bi 0.500000000000000     0.000000000000000     0.000000000000000 Bi 0.000000000000000     0.500000000000000     0.000000000000000 Bi 0.500000000000000     0.500000000000000     0.000000000000000 Bi 0.000000000000000     0.000000000000000     0.500000000000000 Bi 0.500000000000000     0.000000000000000     0.500000000000000 Bi 0.000000000000000     0.500000000000000     0.500000000000000 Bi 0.500000000000000     0.500000000000000     0.500000000000000 Fe 0.250000000000000     0.250000000000000     0.250000000000000 Fe 0.750000000000000     0.250000000000000     0.250000000000000 Fe 0.250000000000000     0.750000000000000     0.250000000000000 Fe 0.750000000000000     0.750000000000000     0.250000000000000 Fe 0.250000000000000     0.250000000000000     0.750000000000000 Fe 0.750000000000000     0.250000000000000     0.750000000000000 Fe 0.250000000000000     0.750000000000000     0.750000000000000 Fe 0.750000000000000     0.750000000000000     0.750000000000000 O  0.187667999289205     0.312332000710795     0.000000000000000 O  0.812332000710795     0.187667999289205     0.000000000000000 O  0.312332000710795     0.687667999289205     0.000000000000000 O  0.687667999289205     0.812332000710795     0.000000000000000 O  0.312332000710795     0.187667999289205     0.500000000000000 O  0.687667999289205     0.312332000710795     0.500000000000000 O  0.187667999289205     0.812332000710795     0.500000000000000 O  0.812332000710795     0.687667999289205     0.500000000000000 O  0.000000000000000     0.187667999289205     0.312332000710795 O  0.500000000000000     0.312332000710795     0.187667999289205 O  0.000000000000000     0.812332000710795     0.187667999289205 O  0.500000000000000     0.687667999289205     0.312332000710795 O  0.000000000000000     0.312332000710795     0.687667999289205 O  0.500000000000000     0.187667999289205     0.812332000710795 O  0.000000000000000     0.687667999289205     0.812332000710795 O  0.500000000000000     0.812332000710795     0.687667999289205 O  0.312332000710795     0.000000000000000     0.187667999289205 O  0.687667999289205     0.000000000000000     0.312332000710795 O  0.187667999289205     0.500000000000000     0.312332000710795 O  0.812332000710795     0.500000000000000     0.187667999289205 O  0.187667999289205     0.000000000000000     0.812332000710795 O  0.812332000710795     0.000000000000000     0.687667999289205 O  0.312332000710795     0.500000000000000     0.687667999289205 O  0.687667999289205     0.500000000000000     0.812332000710795K_POINTS (automatic) 4 4 4 0 0 0CELL_PARAMETERS (angstrom) 7.8 0.0 0.0 0.0 7.8 0.0 0.0 0.0 7.8Best regards,Luiz G. D. SilveiraUniversidade Federal do Paraná - Brazil_______________________________________________Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso)users mailing list users at lists.quantum-espresso.orghttps://lists.quantum-espresso.org/mailman/listinfo/users
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