Grid lines in EFIELD_CUBE for single molecule

[Gary]

Hello,

I have been running a few issues in calculating the electric field in the z 
direction above a single molecule. 

The issue I have now is that the EFIELD_CUBE seems to have these weird grid 
lines as I move away from the molecule. I am quite certain that these are 
not real, but I cannot identify where the issue is coming from. Is it 
because of the poisson solver? I am currently using PERIODIC NONE, and 
POISSON_SOLVER MT. When I did the calculations with PERIODIC XYZ, this 
issue did not occur, but as I am doing single molecule calculations, the 
system should not be periodic.

Attached is the image of the z-component electric field at z=5Å to 
demonstrate what I mean about grid lines. The units of E(z) is V/Å. 
Attached is also the input file.

Thanks,

Gary
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