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Re^5: Lack of force constants for bending vibrations in the output file

Alex Granovsky

Dear Vyacheslav,

to the best of my understanding, any really "intrinsic" quantity
like frequency or force constant should not depend on the particular
way how it is computed. The frequencies and force constants defined
in the paper by Boatz and Gordon are not "intrinsic" in this sense
as they are the functions of the particular set of internals used
to compute them (and this is discussed in some details in the paper
above). It is mentioned that variations in the values obtained for
bond stretches are less sensitive to the choice of internals. Thus
my guess is the rest is too sensitive to worth printing.

Kind regards,

>yes, I read this article before starting the test calculations of intrinsic frequencies.
>My interest in this class of calculations arose from the need to estimate the parameters of the fragments of structures. The more different parameters I have, the more reliable will be correlations and conclusions.
>I also suspected that the lack of frequencies for angular deformations cannot be random and you have confirmed my suspicions. As for me I do not quite understand why they are not. I don't understand the theory well enough. Perhaps you're right.
>Thank you very much for your comments!
>     Vyacheslav

>On Wed Sep 26 '12 11:32pm, Alex Granovsky wrote
>>Dear Vyacheslav,

>>Did you read the paper below?


>>This paper explains some interesting things on this type of analysis.

>>I only can confirm that this exact printout is by code design.
>>In my opinion, intrinsic force constants as defined in the paper
>>above have very little sense, especially for coordinates other
>>than bond stretches. My guess is thus this is the main reason
>>why they are not printed.  

>>Kind regards,
>>Alex Granovsky

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