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Dear. Dr. Giannozzi,</div>
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Thank you very much for your reply and your time.</div>
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I came across a post that you mentioned low frequency modes tend to have sizable admixture. Is
<b>441.1 cm-1</b> considered in the low frequency range?</div>
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I have a question about structure relaxation for a charged system. Currently, I use A = B = 17.2 A and C = 10. I found that when I increase the size of the unit cell, such as A = B = 18 A and C = 10, the structure relaxation didn't converge, but I didn't have
this issue with netural charge system. Is there anything I should be careful when deaing with charged system?</div>
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Additional, I checked my calculation for other molecules, and compare before and after acoustic sum rule. They all have the similar behavior: high frequency modes have very little changes. In the medium frequency region, one or two modes have a significant
shift in frequency. Below is another example as a reference. I noticed that <b>510.0 cm-1
</b>seems to be shifted up to <b>750.02 cm-1</b> after acoustic sum rule. </div>
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------------------------------------------------------ output from ph.x</div>
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Mode symmetry, C_3h (-6) point group:</div>
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</div>
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freq ( 1- 1) = 49.3 [cm-1] --> A' R</div>
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freq ( 2- 2) = 61.2 [cm-1] --> E'' R</div>
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freq ( 3- 3) = 61.2 [cm-1] --> E''* R</div>
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freq ( 4- 4) = 104.0 [cm-1] --> A'' I</div>
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freq ( 5- 5) = 154.3 [cm-1] --> E' I+R</div>
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freq ( 6- 6) = 154.3 [cm-1] --> E'* I+R</div>
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freq ( 7- 7) = 176.8 [cm-1] --> E'' R</div>
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freq ( 8- 8) = 176.8 [cm-1] --> E''* R</div>
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freq ( 9- 9) = 183.5 [cm-1] --> E' I+R</div>
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freq ( 10- 10) = 183.5 [cm-1] --> E'* I+R</div>
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freq ( 11- 11) = 311.8 [cm-1] --> A'' I</div>
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freq ( 12- 12) = 376.2 [cm-1] --> A' R</div>
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freq ( 13- 13) = 386.9 [cm-1] --> E'' R</div>
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freq ( 14- 14) = 386.9 [cm-1] --> E''* R</div>
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freq ( 15- 15) = 401.7 [cm-1] --> A' R</div>
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freq ( 16- 16) = 435.4 [cm-1] --> E' I+R</div>
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freq ( 17- 17) = 435.4 [cm-1] --> E'* I+R</div>
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freq ( 18- 18) = 510.0 [cm-1] --> A'' I</div>
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freq ( 19- 19) = 638.5 [cm-1] --> E'' R</div>
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freq ( 20- 20) = 638.5 [cm-1] --> E''* R</div>
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freq ( 21- 21) = 790.4 [cm-1] --> A'' I</div>
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freq ( 22- 22) = 823.7 [cm-1] --> E' I+R</div>
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freq ( 23- 23) = 823.7 [cm-1] --> E'* I+R</div>
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freq ( 24- 24) = 883.8 [cm-1] --> E' I+R</div>
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freq ( 25- 25) = 883.8 [cm-1] --> E'* I+R</div>
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freq ( 26- 26) = 908.0 [cm-1] --> A' R</div>
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freq ( 27- 27) = 949.2 [cm-1] --> A' R</div>
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freq ( 28- 28) = 1208.3 [cm-1] --> A' R</div>
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freq ( 29- 29) = 1265.0 [cm-1] --> E' I+R</div>
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freq ( 30- 30) = 1265.0 [cm-1] --> E'* I+R</div>
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freq ( 31- 31) = 1277.9 [cm-1] --> A' R</div>
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freq ( 32- 32) = 1464.3 [cm-1] --> E' I+R</div>
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freq ( 33- 33) = 1464.3 [cm-1] --> E'* I+R</div>
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freq ( 34- 34) = 2581.4 [cm-1] --> E' I+R</div>
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freq ( 35- 35) = 2581.4 [cm-1] --> E'* I+R</div>
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freq ( 36- 36) = 2588.7 [cm-1] --> A' R</div>
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--------------------------------------------------------------------------------- output from dynmat.x</div>
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# mode [cm-1] [THz] IR Raman depol.fact</div>
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1 -0.00 -0.0000 0.0000 3.5089 0.7500</div>
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2 -0.00 -0.0000 0.0000 3.7711 0.7500</div>
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3 -0.00 -0.0000 0.0000 0.4088 0.7500</div>
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4 0.00 0.0000 0.0000 0.5258 0.7500</div>
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5 0.00 0.0000 0.0000 1.1191 0.7500</div>
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6 0.00 0.0000 0.0000 1.8734 0.7500</div>
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7 110.68 3.3181 0.0000 0.1475 0.7500</div>
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8 110.68 3.3181 0.0000 0.1475 0.7500</div>
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9 149.03 4.4677 0.0023 0.0000 0.7500</div>
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10 173.76 5.2092 0.0212 3.3877 0.7500</div>
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11 173.76 5.2092 0.0212 3.3877 0.7500</div>
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12 376.21 11.2784 0.0000 12.7649 0.0354</div>
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13 403.42 12.0943 0.0000 8.2338 0.0521</div>
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14 435.39 13.0525 0.0029 0.8795 0.7500</div>
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15 435.39 13.0525 0.0029 0.8795 0.7500</div>
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16 467.53 14.0163 0.0000 0.8370 0.7500</div>
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17 467.54 14.0164 0.0000 0.8370 0.7500</div>
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18 638.52 19.1422 0.0000 0.0197 0.7500</div>
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19 638.52 19.1422 0.0000 0.0197 0.7500</div>
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20 750.02 22.4850 0.0288 0.0000 0.7500</div>
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21 796.81 23.8877 0.0669 0.0000 0.7500</div>
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22 833.63 24.9916 2.3490 1.3092 0.7500</div>
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23 833.63 24.9916 2.3490 1.3092 0.7500</div>
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24 892.72 26.7630 0.3425 2.8335 0.7500</div>
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25 892.72 26.7630 0.3425 2.8335 0.7500</div>
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26 910.03 27.2821 0.0000 10.4788 0.0820</div>
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27 949.01 28.4507 0.0000 36.9935 0.1382</div>
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28 1208.38 36.2262 0.0000 0.6504 0.1090</div>
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29 1265.06 37.9256 7.4876 0.6427 0.7500</div>
<div style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);" class="elementToProof">
30 1265.06 37.9256 7.4876 0.6427 0.7500</div>
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31 1277.95 38.3118 0.0000 11.7798 0.3737</div>
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32 1465.41 43.9318 16.7623 12.2264 0.7500</div>
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33 1465.41 43.9318 16.7623 12.2264 0.7500</div>
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34 2586.09 77.5290 0.0000 314.9596 0.0756</div>
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35 2586.97 77.5555 0.0932 32.8023 0.7500</div>
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36 2586.97 77.5555 0.0932 32.8412 0.7485</div>
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Thank you very much again for your time,</div>
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Weilun Tang</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Paolo Giannozzi <paolo.giannozzi@uniud.it><br>
<b>Sent:</b> Saturday, November 1, 2025 10:34 AM<br>
<b>To:</b> Quantum ESPRESSO users Forum <users@lists.quantum-espresso.org><br>
<b>Cc:</b> Tang, Weilun [M S E] <weilunt@iastate.edu><br>
<b>Subject:</b> Re: [QE-users] Acoustic Sum Rule Frequency Question</font>
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<div class="PlainText">Maybe your 441 cm-1 mode has a large admixture of a rotational mode?
<br>
This may happen if the supercell is not large enough<br>
<br>
Paolo<br>
<br>
On 11/1/2025 12:55 AM, Tang, Weilun [M S E] via users wrote:<br>
> Dear Quantum Espresso users,<br>
> <br>
> I made a phonon calculation for an isolated molecule using acoustic sum <br>
> rule *asr='zero-dim'. *Then, I compared the phonon modes before and <br>
> after applying the acoustic sum rule. I noticed that there is a mode <br>
> that has a huge change in frequency, as shown below. More specifically, <br>
> the *441.1 cm-1* mode seems to be shifted to *115.30 cm-1 *after <br>
> applying the acoustic sum rule. Is this normal?<br>
> <br>
> For this calculation, I used lower threshold: forc_conv_thr = 1.0D-6, <br>
> etot_conv_thr = 1.0D-6, conv_thr = 1.D-14 for pw.x. And for phx, I use <br>
> tr2_ph=1.0d-18.<br>
> -------------------------------------------------------------<br>
> Below is phonon modes from ph.x:<br>
> <br>
> Mode symmetry, D_3h (-62m) point group:<br>
> freq ( 1- 1) = -27.8 [cm-1] --> A'_2<br>
> freq ( 2- 3) = 65.6 [cm-1] --> E'' R<br>
> freq ( 4- 4) = 103.9 [cm-1] --> A''2 I<br>
> freq ( 5- 6) = 120.4 [cm-1] --> E'' R<br>
> freq ( 7- 8) = 146.2 [cm-1] --> E' I+R<br>
> freq ( 9- 10) = 188.8 [cm-1] --> E' I+R<br>
> freq ( 11- 11) = 367.1 [cm-1] --> A'_1 R<br>
> freq ( 12- 13) = 430.7 [cm-1] --> E' I+R<br>
> freq ( 14- 14) = 441.1 [cm-1] --> A''2 I<br>
> freq ( 15- 15) = 461.4 [cm-1] --> A'_2<br>
> freq ( 16- 17) = 631.9 [cm-1] --> E'' R<br>
> freq ( 18- 18) = 776.4 [cm-1] --> A''2 I<br>
> freq ( 19- 20) = 801.0 [cm-1] --> E' I+R<br>
> freq ( 21- 21) = 907.1 [cm-1] --> A'_1 R<br>
> freq ( 22- 22) = 1101.1 [cm-1] --> A'_2<br>
> freq ( 23- 24) = 1150.0 [cm-1] --> E' I+R<br>
> freq ( 25- 25) = 1189.0 [cm-1] --> A'_1 R<br>
> freq ( 26- 27) = 1337.2 [cm-1] --> E' I+R<br>
> ----------------------------------------------------------------<br>
> Below is output from dynmat.x<br>
> <br>
> Reading Dynamical Matrix from file dmat.ttc<br>
> ...Force constants read<br>
> ...epsilon and Z* read<br>
> ...Raman cross sections read<br>
> Acoustic Sum Rule: || Z*(ASR) - Z*(orig)|| = 1.029894E+00<br>
> Acoustic Sum Rule: ||dyn(ASR) - dyn(orig)||= 2.701556E-01<br>
> A direction for q was not specified:TO-LO splitting will be absent<br>
> <br>
> Polarizability (A^3 units)<br>
> multiply by 0.759092 for Clausius-Mossotti correction<br>
> 262.517180 -0.000000 -0.000000<br>
> -0.000000 262.517180 -0.000000<br>
> 0.000000 0.000000 57.305445<br>
> <br>
> IR activities are in (D/A)^2/amu units<br>
> Raman activities are in A^4/amu units<br>
> multiply Raman by 0.576221 for Clausius-Mossotti correction<br>
> <br>
> # mode [cm-1] [THz] IR Raman depol.fact<br>
> 1 -0.00 -0.0000 0.0000 16.3234 0.7500<br>
> 2 -0.00 -0.0000 0.0000 3355.0146 0.7500<br>
> 3 -0.00 -0.0000 0.0000 1478.4689 0.7500<br>
> 4 0.00 0.0000 0.0000 285.5435 0.7500<br>
> 5 0.00 0.0000 0.0000 873.4000 0.7500<br>
> 6 0.00 0.0000 0.0000 1623.8289 0.7500<br>
> 7 73.38 2.1998 0.0000 696.8190 0.7500<br>
> 8 73.38 2.1998 0.0000 696.8152 0.7500<br>
> 9 115.30 3.4567 0.2787 0.0000 0.7500<br>
> 10 177.24 5.3134 1.7092 44473.2909 0.7500<br>
> 11 177.24 5.3134 1.7092 44473.2914 0.7500<br>
> 12 367.09 11.0050 0.0000 11288132.4685 0.1106<br>
> 13 436.75 13.0934 0.2992 3721.4221 0.7500<br>
> 14 436.75 13.0934 0.2992 3721.4231 0.7500<br>
> 15 462.38 13.8617 0.0000 0.0004 0.7500<br>
> 16 631.59 18.9347 0.0000 13677.2759 0.7500<br>
> 17 631.59 18.9347 0.0000 13677.2842 0.7500<br>
> 18 778.46 23.3377 0.0792 0.0000 0.7500<br>
> 19 802.57 24.0605 12.9665 1800840.5786 0.7500<br>
> 20 802.57 24.0605 12.9665 1800840.5109 0.7500<br>
> 21 907.11 27.1945 0.0000 8355726.6168 0.1191<br>
> 22 1101.10 33.0101 0.0000 0.0000 0.7500<br>
> 23 1150.13 34.4801 26.2055 16251271.1703 0.7500<br>
> 24 1150.13 34.4801 26.2055 16251270.4526 0.7500<br>
> 25 1189.02 35.6458 0.0000 16979.5440 0.2674<br>
> 26 1337.59 40.1000 27.2231 16068754.7864 0.7500<br>
> 27 1337.59 40.1000 27.2231 16068754.1344 0.7500<br>
> <br>
> --------------------------------------------------------------------------------------------------------<br>
> Below is my input file for pw.x<br>
> <br>
> &CONTROL<br>
> calculation = "scf",<br>
> prefix = "ttc",<br>
> pseudo_dir = "/home/weilunt/pseudopotential/norm_conserving/pz",<br>
> outdir = "./tmp",<br>
> forc_conv_thr = 1.0D-6,<br>
> etot_conv_thr = 1.0D-6,<br>
> <br>
> /<br>
> &SYSTEM<br>
> assume_isolated = 'martyna-tuckerman',<br>
> ibrav = 4,<br>
> A = 17.2,<br>
> C = 10,<br>
> nat = 9,<br>
> ntyp = 3,<br>
> ecutwfc = 80.D0, !better 120<br>
> tot_charge = -3,<br>
> occupations = 'fixed',<br>
> /<br>
> &ELECTRONS<br>
> conv_thr = 1.D-14,<br>
> mixing_beta = 0.7,<br>
> electron_maxstep = 200,<br>
> /<br>
> &IONS<br>
> /<br>
> ATOMIC_SPECIES<br>
> S 32.070 S.pz-hgh.UPF<br>
> N 14.007 N.pz-hgh.UPF<br>
> C 12.010 C.pz-hgh.UPF<br>
> ATOMIC_POSITIONS (angstrom)<br>
> S 0.0000000000 -3.0749791762 -0.0000000000<br>
> S -2.6627598154 1.5374395881 -0.0000000000<br>
> S 2.6627598154 1.5374395881 0.0000000000<br>
> N 1.1913527585 -0.6879250817 -0.0000000000<br>
> N -1.1913527585 -0.6879250817 0.0000000000<br>
> N 0.0000000000 1.3757501635 0.0000000000<br>
> C 0.0000000000 -1.3240902237 -0.0000000000<br>
> C -1.1466139383 0.6620951119 0.0000000000<br>
> C 1.1466139383 0.6620951119 0.0000000000<br>
> K_POINTS (automatic)<br>
> 1 1 1 0 0 0<br>
> -----------------------------------------------------------------------------------------<br>
> <br>
> Thank you for your time and your help in advance,<br>
> <br>
> Weilun Tang<br>
> <br>
> <br>
> <br>
> _______________________________________________________________________________<br>
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<br>
-- <br>
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,<br>
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216<br>
<br>
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