Hi, for my statistical mechanics class, I had to calculate all the thermochemistry datas by myself and try to see I if get to the same results as Gaussian. Everything is good except for the zero point energy contribution. For instance, in the Gaussian thermochemistry PDF, they say that the ''Sum of electronic and thermal Free Energies'' (wich you can find easily in the output or in Gaussview) is suppose to be the Gibbs free energy. But its not! In fact the zero point energy is missing and there is nowhere in the output or in GaussView where you can see the correct value. And this true also for Enthalpy and internal energy. In fact we have to ad the zero point energy afterwards, which I think is weird since this is the values we really need. In their pdf Gaussian emphisis that the ZPE is added everywhere by default, but it's not true. My teacher is also suspicious about the software. Do we miss something here? What do you guys take as your G, H and U? And where do you find them. I think we could all be wrong if we forget to ad the zero point energy which is what I think Gaussian does.
Thanks
Hello Mathieu
The Gaussian Output gives you 1. electronic energy, 2. Zero-point correction, 3. enthalpy correction and 4. entropy which you can use to calculate the Free energy
The enthalpy is : internal energy + zero-point correction + enthalpy correction The Free energy is : the enthalpy(calculated above) - Temp*entropy What you have be careful is make sure the units are correct in all cases
Hope this will lead to right answer
Pansy
Hello Mathieu
The Gaussian Output gives you 1. electronic energy, 2. Zero-point correction, 3. enthalpy correction and 4. entropy which you can use to calculate the Free energy
The enthalpy is : internal energy + zero-point correction + enthalpy correction The Free energy is : the enthalpy(calculated above) - Temp*entropy What you have be careful is make sure the units are correct in all cases
Hope this will lead to right answer
Pansy
Dear Mathieu,
To understand about the thermodynamics parameters given in Gaussian output read the below pdf
https://gaussian.com/wp-content/uploads/dl/thermo.pdf
Mainly page number 8-9.
Note: The electronic energy is the last Done energy in the output
Look for the white paper from Gaussian titled "Thermochemistry in Gaussian": http://gaussian.com/thermo/
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