Comparison with Gaussian DFT calculation
MattWa... at gmail.com
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
> 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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