[CP2K-user] [CP2K:18638] Work Function Calculation for Charged Systems:

[ling chen]

Dear [Recipient],

Thank you for your prompt and insightful response to my previous inquiry. 
Your expertise has been truly enlightening! I have three more questions 
that I would like to ask for your guidance on:

1.       I did not explicitly use the dipole and electric field corrections 
in my VASP calculations, but I did enable VASPSol. Does VASPSol come with 
built-in dipole and electric field correction capabilities?

2.       Similarly, when calculating a charged slab using the SCCS implicit 
solvent model in CP2K, the Hartree potential is indeed flattened in the 
vacuum region. However, the work function calculated using this method 
differs significantly from the results obtained using VASP. What could be 
the reason for this discrepancy?

3.       Could you please provide me with the dipole correction statement 
for CP2K?

Thank you in advance for your help, and I look forward to your response.

Best regards,

Ling Chen
On Saturday, April 8, 2023 at 7:55:51 AM UTC+10 Lucas Lodeiro wrote:

Hi,

About the vacuum level, when a charged system is calculated, the charges in 
the slab system interacts with the replica in the "non-periodic" direction, 
creating a electric field itself and making the Hartree potential non plane 
in the vacuum zone... this also happens sometimes for neutral slab systems 
with dipoles into the slab or on the surfaces which do not cancel each 
other. In VASP there are dipoles and electric field corrections to 
accomplish this task without this effect maintaining the 3D periodicity... 
I guess you are using those in your VASP calculations. In CP2K AFAIK there 
is dipole corrections, but do not remember if there is electric field 
correction, but here there is the possibility to turn off the periodicity 
of the cell in the "non-periodical" direction of the slab, maybe this is 
the way you need to go.

Regards - Lucas

El vie, 7 abr 2023 a las 18:38, ling chen (<ling... at adelaide.edu.au>) 
escribió:

Dear Experts,

I am currently working on calculating the work function of a system and 
have encountered a few challenges that I would appreciate your insights on.

For the zero-charge system, my current method involves calculating the 
Hartree energy, taking the value in the vacuum region (usually a horizontal 
line, as shown in the attached figure), and subtracting the Fermi energy 
obtained from the .out file. This approach yields results that agree well 
with those obtained using VASP. 

 However, when dealing with charged systems, such as charge = -2, the 
Hartree energy in the vacuum region becomes a diagonal line (as shown in 
the attached figure). Using the average value and subtracting the Fermi 
energy results in a significant discrepancy compared to the VASP 
calculations. It has been suggested that I use the SCCS implicit water 
model to stabilize the vacuum energy level, which does indeed restore the 
horizontal line in the Hartree energy. However, the calculated work 
function deviates even further from the VASP results.

I am unsure about the cause of this discrepancy and would like to inquire 
if you have any recommendations for calculating the work function in 
charged systems. Additionally, I have noticed that the work function 
calculation is significantly influenced by the CUTOFF and REL_CUTOFF 
parameters in MGRID. What values would you suggest to be appropriate for 
these parameters? 

 I would be grateful for your expertise in addressing these concerns. Thank 
you in advance for your time and assistance. 

Kind Regards,

[image: Screenshot 2023-04-08 073641.png][image: Screenshot 2023-04-08 
073716.png]Ling Chen

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