[Pw_forum] How to choose acoustic-sum-rule?

[stefano de gironcoli]

is your system 0-dim ? is it fully relaxed ?

stefano

On 17/12/2015 15:31, yin li wrote:
> Dear QE community,
>
> I wonder if there is a rule to choose acoustic sum rule. I set very 
> tight convergence criterion for both pw.x (conv_thr = 1.0D-10) and 
> ph.x(tr2_ph=1.0d-16).
>
> When I applied asr="simple", the frequencies of the first 3 modes are 
> not equal to zero, but a relatively small negative value. The 
> low-frequency modes are affected, and there is no change in frequency 
> number of high-frequency modes.
> # mode   [cm-1]    [THz]      IR
>     1     -1.27   -0.0381    0.0000
>     2     -1.02   -0.0306    0.0000
>     3     -0.48   -0.0143    0.0000
>     4     50.74    1.5212    0.0042
>     5     66.71    1.9999    0.0031
>     6     76.72    2.3000    0.1024
>     7     91.30    2.7372    0.0605
>     8     92.44    2.7712    0.2996
>     9    102.29    3.0666    0.2928
>    10    107.09    3.2105    0.0402
>    11    113.55    3.4043    0.3288
>    12    117.59    3.5252    0.5163
>    13    133.35    3.9977    0.0394
>    14    136.70    4.0981    0.2142
>    15    144.03    4.3179    0.4547
>    16    158.41    4.7490    0.0742
>
>
> If I employed asr="zero-dim" , the frequencies of the first 6 modes 
> all become 0. But I found the frequencies of all the modes, even 
> high-frequency modes, were varied.
>
> # mode   [cm-1]    [THz]      IR
>     1     -0.00   -0.0000    0.0000
>     2     -0.00   -0.0000    0.0000
>     3     -0.00   -0.0000    0.0000
>     4     -0.00   -0.0000    0.0000
>     5     -0.00   -0.0000    0.0000
>     6      0.00    0.0000    0.0000
>     7     40.75    1.2216    0.0265
>     8     68.45    2.0520    0.1827
>     9     82.84    2.4836    0.1281
>    10     95.99    2.8778    0.2143
>    11    108.98    3.2671    0.3284
>    12    113.25    3.3951    0.4248
>    13    117.89    3.5342    0.2717
>    14    126.27    3.7854    0.0136
>    15    136.33    4.0872    0.3745
>
> I am specially interested in the low-frequency region (1-4 THz). How 
> could I select acoustic sum rule correctly?
>
> Thank you very much in advance!
>
> Best Regards,
> Yin
> ------------------------------------------------------------------------
> Dr. Yin Li
> Department of Biophysics,Medical School, University of Pecs,
> No.12 Szigeti Street, Pecs, H-7624, HUNGARY
> Phone: +36-72-535271/36271
>
>
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