On Mon, Mar 16, 2020 at 1:53 AM Shen, Ziheng <[email protected]> wrote:
> > 1) May I ask is there any literature that can prove it’s feasible to > neglect the small frequencies? > no idea, but you can easily verify whether the neglect of almost-zero frequencies has any effect: if you impose the ASR on dynamical matrices, only frequencies of translational modes (and of rotational ones for a molecule) should change, while all other frequencies should stay almost the same. 2) I saw you also replied to others that “nat_todo” does not make any > sense, but there were still people claimed that they got some useful > results. I read from some books (like the one written by D.Sholl) saying > that it’s possible to calculate only frequencies of adsorbates which could > save computational resources. Some other ab initial calculation software > (like VASP) also have similar functions to calculate adsorbates only. Why > is “nat_todo” not working here? > Presumably it doesn't work because it is not sufficient to just ignore all surface atoms and compute the dynamical matrix restricted to adsorbate atoms only. I guess there are tricks to approximated phonons for an adsorbate on a surface by computing a "reduced" dynamical matrix for the adsorbate only, in which the information on the adsorbate-surface interactions is "refolded", but I don't know any. This same question has been asked over and over again in the list and nobody (that I remember) ever gave an answer. Paolo Best regards Ziheng Shen PhD student @ Georgia Institute of Technology On Mar 15, 2020, at 7:00 AM, [email protected] wrote: On Fri, Mar 13, 2020 at 4:22 AM Shen, Ziheng <[email protected]> wrote: 1) When doing frequency analysis for molecules, I expected to get zero or extremely small value for the first six frequencies (i.e. translational & rotational modes). According to suggestions from those previously posted problems, I tried to apply more restrict convergence thresholds and ASR. It seems that ASR help a lot to reduce the number. But I still got frequencies at ~50 level. Is it possible to completely remove those small values? Or are those values small enough to be neglected? They are small enough to be neglected. They can be removed by applying the ASR to the computed dynamical matrix. See the various kinds of ASR in codes "dynmat" and "matdyn", in particular the "zero-dim" one. Note that more sophisticated ASR than "simple" can be surprising slow. 2) My ultimate goal is to perform frequency analysis for adsorbate so that I can both determine transition state structures and apply ZPE corrections. I tried to use ?nat_todo? to fix the surface atoms and only did calculation for adsorbate (CH in my case). I got crazy result (~10000 cm-1) when using large tr2_ph, and got improved results when I decrease the threshold. But I still got fairly large translational & rotational frequencies like below I don't think you will obtain anything sensible by fixing the surface atoms and making the calculation for the adsorbate atoms only Paolo freq ( 1) = -25.618746 [THz] = -854.549399 [cm-1] freq ( 2) = -7.333895 [THz] = -244.632409 [cm-1] freq ( 3) = -6.696884 [THz] = -223.383991 [cm-1] freq ( 4) = -6.248674 [THz] = -208.433322 [cm-1] freq ( 5) = -4.947831 [THz] = -165.041892 [cm-1] freq ( 6) = -2.014699 [THz] = -67.203109 [cm-1] freq ( 37) = 0.571458 [THz] = 19.061786 [cm-1] freq ( 38) = 5.754719 [THz] = 191.956759 [cm-1] freq ( 39) = 16.488930 [THz] = 550.011494 [cm-1] freq ( 40) = 16.563150 [THz] = 552.487199 [cm-1] freq ( 41) = 18.255969 [THz] = 608.953585 [cm-1] freq ( 42) = 56.121326 [THz] = 1872.005923 [cm-1] What does negative translational frequencies indicate, is it possible to eliminate these imaginary numbers (like using more restrict threshold)? And does my result indicate that my structure is most probably not a transition state since all the other frequencies are positive? I?m attaching the input file of pw.x &ph.x below: =========================scf input, structure obtained from neb.x======================== &CONTROL Calculation='scf', restart_mode='from_scratch', prefix = "Ni_ch_ts" outdir = "./ts/tmp", pseudo_dir = "./pseudo", tstress = .true. verbosity = 'high' tefield = .true. dipfield = .true. / &SYSTEM ibrav = 0, nat = 14, ntyp = 3, ecutwfc = 65, ecutrho = 650, Occupations='smearing', smearing='mp', degauss=0.01, nspin=2, starting_magnetization(1)=0.2, eamp = 0.0 edir = 3 emaxpos = 0.95 eopreg = 0.05 / &ELECTRONS electron_maxstep=250, conv_thr = 1.D-10, mixing_beta = 0.1, / ATOMIC_SPECIES Ni 58.69 ni_pbe_v1.4.uspp.F.UPF C 12 C.pbe-n-kjpaw_psl.1.0.0.UPF H 1 H.pbe-kjpaw_psl.1.0.0.UPF CELL_PARAMETERS { angstrom } 4.9667177200 0.0000000000 0.0000000000 2.4833588600 4.3013037190 0.0000000000 0.0000000000 0.0000000000 20.000000000 ATOMIC_POSITIONS { angstrom } Ni 0.0000000000 0.0000000000 7.9723500000 Ni 1.2416800000 2.1506500000 7.9723500000 Ni 2.4833600000 0.0000000000 7.9723500000 Ni 3.7250400000 2.1506500000 7.9723500000 Ni 2.4833600000 1.4337700000 10.0000000000 Ni 3.7250400000 3.5844200000 10.0000000000 Ni 4.9667200000 1.4337700000 10.0000000000 Ni 6.2084000000 3.5844200000 10.0000000000 Ni 1.2281125212 0.7413038538 12.1124602290 Ni 2.4833613443 2.9495126082 12.0722664849 Ni 3.7386101535 0.7413040204 12.1124604793 Ni 4.9667205066 2.8946406480 11.9560276983 C 2.4833610952 1.4972020489 13.1166864267 H 2.4833559794 3.1940064219 13.5465576823 K_POINTS { automatic } 6 6 1 0 0 0 =======================================ph.x input======================================= phonons of CH on metal Ni at Gamma &inputph tr2_ph=1.0d-16, prefix='Ni_ch_ts', epsil=.false., amass(1)=58.69, amass(2)=12.011, amass(3)=1.0, alpha_mix(1)=0.1, outdir='./tmp/', fildyn='CH.dynG', nat_todo= 2, / 0.0 0.0 0.0 13 14 Thanks in advance for anyone that could give suggestions to me! Best regards Ziheng Shen PhD student @ Georgia Institute of Technology _______________________________________________ > Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) > users mailing list [email protected] > https://lists.quantum-espresso.org/mailman/listinfo/users -- Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche, Univ. Udine, via delle Scienze 208, 33100 Udine, Italy Phone +39-0432-558216, fax +39-0432-558222
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