Comparison with Gaussian DFT calculation

Matt W MattWa... at
Mon Jan 23 21:59:51 UTC 2017


it looks like you cell is very small. Unlike Gaussian CP2K tends to run 
with atoms periodically repeated inside a box. Your's is about 5x5x5 
Angstrom^3. Probably you have some steric clashes between images of the 
molecule, and likely these are different between the conformers.


On Monday, January 23, 2017 at 8:05:24 PM UTC, Babgen Manookian wrote:
> Hello all,
> I am new to CP2K and am working on making the transfer from Gaussian09. I 
> am trying to match energy calculations between the two programs but am 
> having trouble so I hope someone can help me.
> System: Just for testing purposes, I want to calculate the energy 
> difference between chair and boat conformations for a cyclohexane molecule.
> Gaussian09: for my Gaussian calculations I am using DFT with BLYP 
> functional and a 6-31G* basis set. Using this setup I obtain an energy 
> difference of ~34 kJ/mol which is in fair agreement with a textbook value 
> of ~30 kJ/mol.
> CP2K: For CP2K I am using DZVP-GTH-BLYP basis sets and GTH-BLYP 
> pseudopotentials for both carbon and hydrogen atoms. Pretty much all other 
> input parameters are set to default values or in accordance to the ones 
> given in the Si test files found on the CP2K website. The input file is 
> attached for further detail if needed. With this set-up I am obtaining an 
> energy difference of ~288 kJ/mol. Clearly this value is way off the 
> expected value and my Gaussian-obtained value and I am totally lost as to 
> why.
> I have done these calculations with different values for cutoffs and 
> different basis sets and in all cases I get a similar result where the 
> difference between the two methods is roughly ten-fold. I am wondering if 
> there may be something trivial that I am doing that is causing this.
> Any sort of insight will be truly appreciated.
> Thank you very much in advance.
> Babgen Manookian
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