[CP2K-user] Large difference in lattice constant between CP2K and VASP

ASSIDUO Network lenardc... at gmail.com
Mon Jan 18 13:46:38 UTC 2021

Thank you very much for your response. I will definitely look into k-point 
grids and apply your recommendations. See if that changes things.

Most of the flags/values I used were from my supervisor's (other) student, 
who recommended these to me. I'm still very new to CP2K, so I am still 
learning what to use/not to use.
On Monday, January 18, 2021 at 3:33:21 PM UTC+2 fa... at gmail.com wrote:

> Hi,
> you are running the optimization without a k-point grid, so you only 
> consider the gamma point. To get a more reasonable result add
>     &KPOINTS
>       SCHEME MONKHORST-PACK 20 20 20
> to the &DFT section. Adjust the number of kpoints to your needs. When 
> using k-points you should probably change METHOD DIRECT_P_MIXING to METHOD 
> A few more hints:
> with DIAGONALIZATION you dont need the outer_scf section and ADDED_MOS 100 
> seems excessive.
> @SET SCF_CONV 1E-5 is rather inaccurat, I'd recomment decreasing that to 
> 1e-6 or 1e-7 even.
> Is there a specific reason to decrease @SET GRIDS 3 from the default? That 
> should not be needed.
> When performing simulations with a variable cell size it's recommended to 
> include a &CELL_REF section. Set these lattice vectors longer than the 
> maximum value that you expect during the simulation (for your real cell).
> Cheers,
> Fabian
> On Monday, 18 January 2021 at 14:16:16 UTC+1 ASSIDUO Network wrote:
>> Hi there, I am trying to calculate the lattice constant of bulk Au using 
>> CP2K (cell optimization is fine). I have included my input file below.
>> With CP2K, I get a lattice constant around 4.6 Å, while with VASP I get a 
>> value of 4.17 Å. The literature lattice constant for bulk Au should be 
>> around 4.08 Å. Why do I get such a massive difference in value between CP2K 
>> and VASP/literature?
>> What would you advise I do with my calculation to improve my results? The 
>> largest basis set available for Au (with CP2K) is TZV2P. My supervisor 
>> wants me to use the GTH-PBE potential, so I can't change that.
>> Thank you for your help in advance :)
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