Mr. Zoric,

Presumably not. Compare your DFT results with CASSCF ones.

Thank you, Dr. Bojidarka B. Ivanova !

Thank you, Prof. Andy Ohlin

For small molecules as O2 and H2, the thermal correction to the Gibbs energy is negative.

Thank you, Prof. Agusti Lledos !

Your problem is poorly defined. Quantum chemistry calculations is not something that would yield Gibbs free energy. Only a combination with a statistical thermodynamics model can do that. Based on what you mention I guess you used values calculated by Gaussian, which means probably RRHO model was used. This model might be inadequate for your molecules whatever they are. Even if there are not any internal rotations, the quantum-chemistry calculated frequencies have to be scaled to correct for anharmonicity (or calculated anharmonically) - but Gaussian ignores that.

The so-called "entropy " doesn't exist at all.

During the process of deriving the so-called entropy, in fact, ΔQ/T can not be turned into dQ/T. That is, the so-called "entropy " doesn't exist at all.

The so-called entropy was such a concept that was derived by mistake in history.

It is well known that calculus has a definition,

any theory should follow the same principle of calculus; thermodynamics, of course, is no exception, for there's no other calculus at all, this is common sense.

Based on the definition of calculus, we know:

to the definite integral ∫T f(T)dQ, only when Q=F(T), ∫T f(T)dQ=∫T f(T)dF(T) is meaningful.

As long as Q is not a single-valued function of T, namely, Q=F( T, X, …), then,

∫T f(T)dQ=∫T f(T)dF(T, X, …) is meaningless.

1) Now, on the one hand, we all know that Q is not a single-valued function of T, this alone is enough to determine that the definite integral ∫T f(T)dQ=∫T 1/TdQ is meaningless.

2) On the other hand, In fact, Q=f(P, V, T), then

∫T 1/TdQ = ∫T 1/Tdf(T, V, P)= ∫T dF(T, V, P) is certainly meaningless. ( in ∫T , T is subscript ).

We know that dQ/T is used for the definite integral ∫T 1/TdQ, while ∫T 1/TdQ is meaningless, so, ΔQ/T can not be turned into dQ/T at all.

that is, the so-called "entropy " doesn't exist at all.

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Why did the wrong "entropy" appear ?

In summary , this was due to the following two reasons:

1) Physically, people didn't know Q=f(P, V, T).

2) Mathematically, people didn't know AΔB couldn‘t become AdB directely .

If people knew any one of them, the mistake of entropy would not happen in history.

Please read my paper and those answers of the questions related to my paper in my Projects.

https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity

1. General philosophy principle: internal cause (thermophysical property of working fluid) determines external performance (Carnot efficiency).

2. The second law of thermodynamics holds that Carnot efficiency has nothing to do with the thermophysical properties of working medium.

3. The second law of thermodynamics violates the general principle of life. And it's self contradictory.

4. Please see the picture and link:

https://www.researchgate.net/publication/352708795_The_contradiction_of_the_second_law_of_thermodynamics