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