Hello professor,

Attaching a copy of PDF, hope it will be useful for you.

thank you.

Hi Professor,

This might be useful as well:

http://www.gaussian.com/g_whitepap/thermo/thermo.pdf

See Section 4.3.  You can't have the enthalpy of formation of a compound directly from a gaussian output file, you need a bit more. The example in the link gives you the spirit of it, and it is done with the atomization scheme. Sometimes people prefer using isodesmic reactions which will minimize errors.

Hope this helps.

Regards

Hi Thion,

Thanks for your reply. Now, What is the method (DFT or some other) gives better results which should almost equal to experimental values. 

This depends on the system you're studying and the ressources you have. If you're working on a huge protein, then it will probably be difficult to do better than DFT because of the computational cost.

For smaller molecules, you can do better than DFT alone. I usually go for compound methods (G3B3 or CBS-QB3) and it works quite well. They are based on DFT for geometry optimization and vibrationnal analysis but they also includes several single point calculations with high level ab initio methods. If you're working on a system with a reasonable size and with no "exotic" atoms, then you should be fine with that.

Hi Thion,

I will try. thanks for your reply

Hi Thion,

I tried to calculate the HOF as per your suggestion. I saw the work example in thermo.pdf, But i cant fix the product and reactant for the molecule.  Any suggestion....