[CP2K-user] [CP2K:18633] Work Function Calculation for Charged Systems:

[ling chen]

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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