[Pw_forum] phonon Calculation

[Paolo Giannozzi]

On Sat, 2014-05-03 at 17:44 +0530, Saied Md Pratik wrote:

> If I don't mention asr='zero-dim' in the input section then also I am
> not getting the frequencies correctly. Now I am getting the following
> frequencies

plot the corresponding modes and maybe you will understand why they are
unstable

P.

> --------------------------------------
> # mode   [cm-1]    [THz]      IR
>     1   -132.06   -3.9590    0.1498
>     2   -131.77   -3.9503    0.1486
>     3   -109.35   -3.2782    0.0031
>     4   -108.74   -3.2599    0.0032
>     5     91.54    2.7443    0.0511
>     6    127.22    3.8141    0.0142
>     7    153.76    4.6095    0.0003
>     8    164.03    4.9174    5.4586
>     9    164.06    4.9185    5.4543
>    10    190.74    5.7182    4.0762
>    11    191.78    5.7493    0.0010
>    12    191.95    5.7544    0.6314
>    13    380.90   11.4192    0.0000
>    14    395.35   11.8522    0.0004
>    15    397.38   11.9132    0.0001
>    16    410.55   12.3081    0.0022
>    17    412.54   12.3677    0.0019
>    18    420.67   12.6114    0.0001
>    19   1398.48   41.9255    0.0328
>    20   1407.66   42.2007    5.2353
>    21   1408.10   42.2137    5.5635
>    22   1414.41   42.4029    0.0151
>    23   1414.84   42.4158    0.3427
>    24   1435.81   43.0446    7.0296
>    25   1635.17   49.0210    0.0000
>    26   1666.27   49.9536    0.0000
>    27   1685.50   50.5300    0.0001
>    28   1686.11   50.5484    0.0000
>    29   3052.32   91.5064    0.5011
>    30   3066.46   91.9303    3.0260
>    31   3082.41   92.4082   45.2275
>    32   3086.97   92.5451   19.4732
>    33   3091.92   92.6934   41.1318
>    34   3095.54   92.8020   33.9297
>    35   3103.29   93.0342   38.8619
>    36   3154.67   94.5747   67.2231
> --------------------------------------------------------------------
> 
> 
> Thanking you.
> Pratik
> 
> 
> 
>         
>         On Fri, 2014-05-02 at 14:09 +0530, Saied Md Pratik wrote:
>         
>         > NH4Br crystal
>         
>         > asr='zero-dim'
>         
>         if it is a real crystal, you shouldn't use 'zero-dim'.
>         If it is a molecule in a supercell, you may have unstable
>         (and physically irrelevant) libration modes
>         
>         >    celldm(1) = 1.890359168
>         
>         putting into celldm(1) the a.u. to A conversion factor
>         is a bad habit in my opinion, and ot doesn't make sense
>         if you specify your cell vectors in A:
>         
>         > CELL_PARAMETERS angstrom
>         >    5.633079685   0.000000000   0.000000000
>         >    0.000000000   5.633079685   0.000000000
>         >    0.000000000   0.000000000   3.982678150
>         
>         P.
>         
>         --
>         Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
>         Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>         Phone +39-0432-558216, fax +39-0432-558222
>         
>         
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222