THERMOCHEMISTRY

[Gerard pareras niell]

Hello,

I am working with a set of polymers, and I would like to obtain the correction for Gibbs energy.

However, when performing the vibrational analysis, the term for the entropy is not calculated as: 

VIB| Entropy [kJ/ (mol K)]: NaN

and so, Gibbs correction:

VIB| Gibbs energy correction [kJ/mol]: NaN

I guess that the entropy is not computed due to there are some imaginary frequencies.

My questions are:

Can those imaginary frequencies be avoided during the calculation of the thermochemistry?

In principle the system should be a local minimum however there are some small negative vibrations.

if not, how is then possible to calculate the Gibbs energy for a transition state, where we indeed want those negative frequencies?

Please find attached here the files for input and output.

Thank you very much in advance.

best,

Gerard

[Geng Sun]

Dear Gerard,

I am not sure how cp2k deals with the negative vibrational frequencies, but I do think  the NaN stems from the small/negative frequencies.

In my opinion, if the polymer system has many soft modes, you may not compute the entropy reliably from the vibrational analysis because of the anharmonic effect.

If you are sure that you can trust the vibrational analysis, you will have to optimize your structure with better accraucy (both electronic scf and geometrical optimizations).

Best,
Geng

------------------ 原始邮件 ------------------

发件人: "cp2k" <gpar...@gmail.com>;

发送时间: 2021年7月30日(星期五) 晚上11:45

收件人: "cp2k"<cp...@googlegroups.com>;

主题: [CP2K:15807] THERMOCHEMISTRY

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