Comparison with Gaussian DFT calculation

Babgen Manookian manoo... at gmail.com
Mon Jan 23 21:05:24 CET 2017


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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