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saja.mahdizadeh
Nov 12, 2020, 10:19:34 AM11/12/20
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Hi all,
Why did I get zero frequency for the first 6 vibrational modes after QMMM optimization?
the output is pasted below.
----------------------------------------------------------------------------
Normal Eigenvalue || Projected Derivative Dipole Moments (debye/angs)
Mode [cm**-1] || [d/dqX] [d/dqY] [d/dqZ]
------ ---------- || ------------------ ------------------ -----------------
1 -0.000 || 0.083 0.085 -0.218
2 -0.000 || 0.081 -0.111 -0.160
3 -0.000 || -0.170 -0.271 0.232
4 -0.000 || -0.016 0.076 -0.057
5 0.000 || -0.171 0.040 0.231
6 0.000 || 0.027 -0.104 0.003
7 638.720 || 0.436 1.188 -1.167
8 950.337 || -0.087 0.175 1.350
9 1107.860 || 0.075 -0.180 -0.258
10 1211.710 || 0.139 0.740 -0.117
11 1538.393 || 0.234 0.637 0.203
12 1592.991 || 0.416 0.875 0.151
13 1650.177 || 0.140 0.577 0.292
14 2191.771 || 0.204 -0.304 -0.574
15 2256.408 || 0.068 0.321 -0.060
16 3153.315 || -0.107 -0.204 0.669
17 3235.992 || -0.417 0.271 -0.246
18 3582.340 || -0.189 0.192 0.198
----------------------------------------------------------------------------
Sibo Lin
Nov 12, 2020, 12:49:27 PM11/12/20
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This is normal. A freq calc can be thought of as wiggling each atom a little bit in the x, y, and z directions. There are linear combinations of these atomic wiggles that correspond with translation of the entire unaltered molecule in the x, y, or z direction. These are three zero freq vibrations. The other three correspond to rotation of the unaltered molecule about the x y and z axes. You’ll see these zero freq vibrations for all molecules (except atoms and linear molecules will have less zero freq modes)
saja.mahdizadeh
Nov 12, 2020, 1:27:20 PM11/12/20
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Thank you Sibo for the explanation.
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