Wrong total charge in calculations with thin slabs

[lowsfer]

Hi, I have been playing with slab calculation. I started with thickness convergence test. I used zinc-blende InP and the slab is composed of the <110> stom layers. The interesting thing is that the work function jumped from 3.36eV to 4.56eV when I change the number of atom layers from 10 to 11. But the work function was constant from 4 to 10 layers, or from 11 to 20 layers.

This should not happen so I looked into CHGCAR. I did a integration over the whole supercell I used, and normalised the charge to number of atoms. I found that for less than 10 layers, the charge per atom is 1.5; while for more than 11 layers, the charge per atom is 4.0. The later one should be correct since it is InP.

I can make sure I only changed POSCAR. I only changed the number of atoms and vacuum thickness in POSCAR. INCAR, POTCAR and KPOINTS are kept identical. Vacuum thickness has also been tested and I found it is irrelevant.

POSCAR for 10 layers

Code: Select all

In??????P
4.242463011
1.4142135624????0???????0
0???????1???????0
0???????0???????10
10?10
cartesian
0???????0???????0
0.7071067812????0.5?????0.5
0???????0???????1
0.7071067812????0.5?????1.5
0???????0???????2
0.7071067812????0.5?????2.5
0???????0???????3
0.7071067812????0.5?????3.5
0???????0???????4
0.7071067812????0.5?????4.5
0.3535533906????0.5?????0
1.0606601718????0???????0.5
0.3535533906????0.5?????1
1.0606601718????0???????1.5
0.3535533906????0.5?????2
1.0606601718????0???????2.5
0.3535533906????0.5?????3
1.0606601718????0???????3.5
0.3535533906????0.5?????4
1.0606601718????0???????4.5

POSCAR for 11 layers

Code: Select all

In??????P
4.242463011
1.4142135624????0???????0
0???????1???????0
0???????0???????11
11?11
cartesian
0???????0???????0
0.7071067812????0.5?????0.5
0???????0???????1
0.7071067812????0.5?????1.5
0???????0???????2
0.7071067812????0.5?????2.5
0???????0???????3
0.7071067812????0.5?????3.5
0???????0???????4
0.7071067812????0.5?????4.5
0.3535533906????0.5?????0
1.0606601718????0???????0.5
0.3535533906????0.5?????1
1.0606601718????0???????1.5
0.3535533906????0.5?????2
1.0606601718????0???????2.5
0.3535533906????0.5?????3
1.0606601718????0???????3.5
0.3535533906????0.5?????4
1.0606601718????0???????4.5
0.3535533906????0.5?????5

[support_vasp]

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