DDAP charges

[Alex]

Hi all,

I am trying to calculate DDAP partial charges just to get a sense of what 
the Blochl approach produces. My model system is a rectangular boron 
nitride monolayer (about 2 nm by 2 nm) and I am following the setup 
here: https://pubs.acs.org/doi/10.1021/acs.jpclett.7b03443

My setup is CELL_OPT with PBE + D3 corrections, GTH potentials, and 
MOLOPT-SR basis sets, all defaults in the DENSITY_FITTING section. For an 
intact periodic sheet, i get nitrogen and boron charges of -0.915 and 
+0.915, respectively -- reasonably close to +/-0.907 reported in the paper 
above, so all is more or less reasonable. Well, not quite. 

If I create a defect by removing a single unit cell of atoms (a 
nearest-neighbor BN pair) at the center of the sheet, the charge 
distribution changes _throughout the entire sheet_ with charges +/-0.75 far 
away from the defect. This does not seem to make much sense, as the effects 
of this vacancy should not extend this far in terms of atomic ionicity. Am 
I wrong about this? Can someone comment, please?

Thanks,

Alex
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