Comparison with Gaussian DFT calculation

Matt W MattWa... at
Thu Jan 26 18:44:18 UTC 2017


you need to turn off periodicity in both the CELL section (which controls 
the generation of atoms), and in the POSSION section, where electrostatics 
are calculated.


and periodic none in the CELL section. Your molecule needs to be in the 
center of the cell, not near the edges.

For a molecule that is not very polar, the artifacts from running 
periodically vs isolated should go very quickly as the box size increases.


On Thursday, January 26, 2017 at 5:42:03 PM UTC, Babgen Manookian wrote:
> Hey Matt,
> Thank you for the answer. I am working on running the calculations with 
> bigger cell size at the moment. In the meantime, I am wondering if there is 
> a way to turn off the periodicity in CP2K. I tried using the keyword 
> PERIODIC NONE but got the exact same results.
> Any help will be much appreciated it.
> Thank you,
> Bobby
> On Monday, January 23, 2017 at 4:59:51 PM UTC-5, Matt W wrote:
>> Hi,
>> 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.
>> Matt
>> 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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