Issue with charged adsorption energy calculations

[jess_white]

Hi,

I am having some issues with using charged cells for adsorption energies.

Is it correct that the adsorption energy will be:

Ead = charged adsorbate on mineral surface energy - energy of charged adsorbate - energy of mineral surface

I think the issue is the charged adsorbate on the mineral surface energy which I will attach on this thread. Maybe the INCAR doesn't make sense? I changed the NELECT to have 2 more electrons as carbonate has a charge of 2-.

Many thanks,
Jess

[fabien_tran1]

Hi,

Calculations on charged slabs are not trivial. As mentioned at NELECT and Electrostatic_corrections, the total energy does not converge with respect to the size of the vacuum.

However, note that the KERNEL_TRUNCATION/LTRUNCATE tag, that allows to switch off the electrostatic interactions along non-periodic dimensions, is available since VASP.6.5.0 (with a bug corrected in VASP.6.5.1). That may well provide a solution to your problem. Discussions on the kernel-truncation method can be found at:
wiki/index.php/Charged_systems_with_den ... nal_theory
forum/viewtopic.php?t=19937
forum/viewtopic.php?t=19968

[jess_white]

Hi Fabien,

Thank you for your response! I have tried the other method and have had further issues. I just submitted another topic for it but I can add that to here.

Hi,

I am currently trying to do charged calculations as I have a CO3^2- molecule adsorbing onto a diopside surface. To do the charge I initially did dipoles but then saw that this would be a better method (you will see lots of # in the INCAR of things I tried).

What I am finding is that with the calculations they are very crazy when I consider the KERNEL_TRUNCATION for both the adsorbed surface and the clean surface. When I commented out the KERNEL in the INCAR for the surface it goes back to normal so I know its something to do with the KERNEL_TRUNCATION addition.

I have done the following:
- removed the dispersion forces
- increased vacuum as I know that was a previous issue
- have ISPIN = 1 and ISPIN = 2 (both gained same results)

I even changed the surface normal to see if that would do anything but still got the crazy results. Any help would be greatly appreciated!