[Pw_forum] Confused about vibrational modes of isolated molecule from ph.x
degironc
degironc at sissa.it
Mon Nov 20 11:25:07 CET 2006
did you relaxed the structure ?
These are the forces I get with your input [a typical threshold for a
structural relaxation is
forc_conv_thr REAL ( default = 1.0D-3 ) ].
stefano
Forces acting on atoms (Ry/au):
atom 1 type 2 force = -0.06870568 0.00011605 0.00070580
atom 2 type 1 force = 0.00057171 -0.00133033 0.00026104
atom 3 type 2 force = -0.03470840 0.06008037 0.00060235
atom 4 type 1 force = -0.00200170 -0.00052894 -0.00023669
atom 5 type 2 force = 0.03477692 0.05989867 -0.00004091
atom 6 type 1 force = 0.00029793 0.00027534 -0.00032982
atom 7 type 2 force = 0.06862846 -0.00002844 -0.00054894
atom 8 type 1 force = -0.00256825 0.00128897 -0.00025706
atom 9 type 2 force = 0.03495275 -0.06050673 -0.00040942
atom 10 type 1 force = -0.00020204 0.00131722 0.00025463
atom 11 type 2 force = -0.03450037 -0.05925204 0.00020053
atom 12 type 1 force = 0.00345864 -0.00133014 -0.00020152
Total force = 0.169286 Total SCF correction = 0.000107
stefano
Jin Zhang wrote:
> Dear MMC,
>
> The supercell I used is a simple cubic one (let ibrav=8
> celldim(1,2,3)=20bohr). Because the molecule is isolated, I think the
> kpoint sampling should be irrelevant. And I used gamma point for the
> calculation.
>
> I increased ecut to 25Ry, and celldim to 30bohr) the number of
> negative modes increase by 9 (to 21modes)!
> OMG, there must be sth wrong!
> I'll attach my input and see if someone can give some comments.
> !-----------------------omega-------------------
> omega( 1) = -123.660534 [THz] = -4124.898815 [cm-1]
> omega( 2) = -122.070631 [THz] = -4071.865015 [cm-1]
> omega( 3) = -109.408034 [THz] = -3649.483445 [cm-1]
> omega( 4) = -103.611190 [THz] = -3456.120267 [cm-1]
> omega( 5) = -100.288151 [THz] = -3345.274863 [cm-1]
> omega( 6) = -86.921490 [THz] = -2899.408087 [cm-1]
> omega( 7) = -86.648147 [THz] = -2890.290289 [cm-1]
> omega( 8) = -78.536226 [THz] = -2619.703943 [cm-1]
> omega( 9) = -63.552993 [THz] = -2119.913758 [cm-1]
> omega(10) = -60.437624 [THz] = -2015.995524 [cm-1]
> omega(11) = - 59.290658 [THz] = -1977.736621 [cm-1]
> omega(12) = -59.022664 [THz] = -1968.797246 [cm-1]
> omega(13) = -58.953578 [THz] = -1966.492750 [cm-1]
> omega(14) = -46.326804 [THz] = -1545.306104 [cm-1]
> omega(15) = -31.263942 [THz] = -1042.859776 [cm-1]
> omega(16) = -31.093207 [THz] = -1037.164629 [cm-1]
> omega(17) = -27.758798 [THz] = -925.939988 [cm-1]
> omega(18) = - 27.694407 [THz] = -923.792135 [cm-1]
> omega(19) = -24.097859 [THz] = -803.823410 [cm-1]
> omega(20) = -20.675736 [THz] = -689.672916 [cm-1]
> omega(21) = -20.064562 [THz] = -669.286187 [cm-1]
> omega(22) = 15.218497 [THz] = 507.637805 [cm-1]
> omega(23) = 16.277849 [THz] = 542.974191 [cm-1]
> omega(24) = 20.249558 [THz] = 675.457041 [cm-1]
> omega(25) = 21.320279 [THz] = 711.172668 [cm-1]
> omega(26) = 22.104349 [THz] = 737.326626 [cm-1]
> omega(27) = 23.427206 [THz] = 781.452687 [cm-1]
> omega(28) = 30.392570 [THz] = 1013.793763 [cm-1]
> omega(29) = 43.644315 [THz] = 1455.827328 [cm-1]
> omega(30) = 55.006552 [THz] = 1834.833267 [cm-1]
> omega(31) = 57.997854 [THz] = 1934.613035 [cm-1]
> omega(32) = 61.898591 [THz] = 2064.728462 [cm-1]
> omega(33) = 68.862483 [THz] = 2297.020463 [cm-1]
> omega(34) = 68.979827 [THz] = 2300.934652 [cm-1]
> omega(35) = 69.303015 [THz] = 2311.715098 [cm-1]
> omega(36) = 69.697807 [THz] = 2324.884051 [cm-1]
>
> On 11/19/06, *Miguel Martínez Canales* < wmbmacam at lg.ehu.es
> <mailto:wmbmacam at lg.ehu.es>> wrote:
>
> Hi Jin,
>
> Jin Zhang escribió:
> > The thing I cannot understand is, there're 12 negative frequencies
> > existing. I know 3 of them are purely translational modes and
> another 3
> > are rotational ones. But what about the rest 6? I'm a little
> confused
> > and hopefully someone can help.
> >
> > The eigenvals are pasted below and thanks in advance!
> >
> > (the result may not be accurate due to a only-15Ry ecut I used,
> but it
> > should not give out qualitative different result)
>
> For a start, I wouldn't think 15 rydbergs is enough. Have you
> tested the
> pseudopotentials for ecut convergence? 25 or 30 would probably be
> a better
> choice. Anyway, what you probably are missing most in your
> calculations is
> k-point sampling convergence. Translational and rotational
> frequencies are
> a bit too large. What happens if you increase your k-point grid?
> Anyway,
> don¡t forget to relax your molecule with the new parametres.
>
> BTW: What kind of cell are you using? I've never done molecular
> normal mode
> calculations but I guess that in the case of bencene using an
> hexagonal
> supercell might make sense.
>
> --
> ----------------------------------------
> Miguel Martínez Canales
> Dto. Física de la Materia Condensada
> UPV/EHU
> Facultad de Ciencia y Tecnología
> Apdo. 644
> 48080 Bilbao (Spain)
> Fax: +34 94 601 3500
> Tlf: +34 94 601 5437
> ----------------------------------------
>
> "The problem with Renault is that they dont have
> the skills to convince FIA that the mass damper
> is just a brake cooler."
>
> Annonymous
>
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>
>
>
> --
> Jin Zhang
> Dep. of Physics,
> Peking Univ.
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