[QE-users] Variation in ph.x results for QE 6.5 and QE 6.4

[Paolo Giannozzi]

ASR is applied by auxiliary code, confusingly named "matdyn.x" and
"dynmat.x"

Paolo


On Mon, Sep 14, 2020 at 9:42 AM Offermans Willem <willem.offermans at vito.be>
wrote:

> Dear QE friends and Paolo,
>
> I’m sorry to break into this mail thread, but could you elaborate a bit on
> “applying acoustic sum rule”.
>
> How is this done?
>
>
>
> Met vriendelijke groeten,
> Mit freundlichen Grüßen,
> With kind regards,
>
>
> Willem Offermans
> Researcher Electrocatalysis SCT
> VITO NV | Boeretang 200 | 2400 Mol
> Phone:+32(0)14335263 Mobile:+32(0)492182073
>
> Willem.Offermans at Vito.be
>
>
> On 14 Sep 2020, at 08:34, Paolo Giannozzi <p.giannozzi at gmail.com> wrote:
>
> Apparently the largest discrepancies come from low-energy modes, in
> particular zero-frequency acoustic modes (those with "negative" frequencies
> that become zero when acoustic sum rule is applied). Even minor changes in
> the way exchange-correlation is computed may lead to surprisingly large but
> unphysical differences for those modes.
>
> Paolo
>
> On Sun, Sep 13, 2020 at 7:54 PM Unmesh Mondal <
> unmesh.mondal at students.iiserpune.ac.in> wrote:
>
>> Dear all,
>> I intend to calculate the vibrational modes of  gas phase HCOOH (formic
>> acid) molecule.
>>
>> The "ph.x" vibrational frequencies (in cm-1) of the system for the two
>> versions of quantum espresso (6.5 and 6.4 : with same compilers) are:
>>              (QE 6.5)           (QE 6.4)
>>     1      -207.654081    -207.686563
>>      2      -63.775769      -61.840758
>>      3      -55.090067      -57.158594
>>      4     -15.183543       -15.903109
>>      5      20.311666        21.386665
>>      6     129.683418       129.214185
>>      7     615.352300        615.209434
>>      8     676.597853        676.547298
>>      9     999.285772        999.331118
>>     10   1071.840671      1071.779138
>>     11   1253.496419      1253.514267
>>     12   1350.618940      1350.925730
>>     13   1735.698557      1735.582574
>>     14    2965.285270     2965.885980
>>     15    3665.961548     3665.948232
>>
>> The maximum difference in any frequency for the two versions is about 2
>> cm-1. My question:
>>  Is the difference of 2 cm-1 within the error limit of ph.x
>> calculations?  What is the accuracy we expect in reporting the vibrational
>> frequency (via ph.x)?
>>
>> Regards and Thanks
>> Unmesh Mondal
>> IISER Pune, India
>>
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>
> --
> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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