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

[Unmesh Mondal]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20200913/58f75593/attachment.html>