[Pw_forum] Confused about vibrational modes of isolated molecule from ph.x
Jin Zhang
jin.zhang.pku at gmail.com
Sun Nov 19 08:29:15 CET 2006
Dear all,
I've tested the supercell approach using ph.x to calculate the vibrational
frequency of a benzene molecule. It works indeed. And I got 36(12*3) eigen
values.
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)
omega( 1) = -75.772470 [THz] = -2527.514330 [cm-1]
omega( 2) = -70.357356 [THz] = -2346.884371 [cm-1]
omega( 3) = -69.734785 [THz] = -2326.117499 [cm-1]
omega( 4) = -60.745067 [THz] = -2026.250783 [cm-1]
omega( 5) = -60.633397 [THz] = -2022.525849 [cm-1]
omega( 6) = -54.624392 [THz] = -1822.085685 [cm-1]
omega( 7) = -53.629434 [THz] = -1788.897259 [cm-1]
omega( 8) = -49.221716 [THz] = -1641.870640 [cm-1]
omega( 9) = -48.767076 [THz] = -1626.705379 [cm-1]
omega(10) = -45.544107 [THz] = -1519.197979 [cm-1]
omega(11) = -40.582868 [THz] = -1353.707753 [cm-1]
omega(12) = -29.501111 [THz] = -984.057687 [cm-1]
omega(13) = 17.297930 [THz] = 577.000669 [cm-1]
omega(14) = 18.430268 [THz] = 614.771652 [cm-1]
omega(15) = 18.978064 [THz] = 633.044293 [cm-1]
omega(16) = 21.573348 [THz] = 719.614207 [cm-1]
omega(17) = 21.661957 [THz] = 722.569926 [cm-1]
omega(18) = 22.212850 [THz] = 740.945851 [cm-1]
omega(19) = 26.603080 [THz] = 887.389115 [cm-1]
omega(20) = 27.163155 [THz] = 906.071359 [cm-1]
omega(21) = 28.988845 [THz] = 966.970217 [cm-1]
omega(22) = 29.897145 [THz] = 997.268046 [cm-1]
omega(23) = 30.039795 [THz] = 1002.026353 [cm-1]
omega(24) = 34.221037 [THz] = 1141.498514 [cm-1]
omega(25) = 35.556617 [THz] = 1186.048959 [cm-1]
omega(26) = 41.365733 [THz] = 1379.821484 [cm-1]
omega(27) = 48.259770 [THz] = 1609.783366 [cm-1]
omega(28) = 51.789502 [THz] = 1727.523303 [cm-1]
omega(29) = 51.871548 [THz] = 1730.260091 [cm-1]
omega(30) = 55.413486 [THz] = 1848.407220 [cm-1]
omega(31) = 85.179130 [THz] = 2841.288830 [cm-1]
omega(32) = 87.544947 [THz] = 2920.204497 [cm-1]
omega(33) = 88.051107 [THz] = 2937.088312 [cm-1]
omega(34) = 89.398003 [THz] = 2982.016222 [cm-1]
omega(35) = 93.664201 [THz] = 3124.322195 [cm-1]
omega(36) = 95.571010 [THz] = 3187.926929 [cm-1]
--
Jin Zhang
Dep. of Physics,
Peking Univ.
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