[QE-users] Negative charge density in slabs

[Marios Georgiou]

Hello,

I have a question about slabs.
I am using QE 7.4.1 (developer edition) for a slab along the z-axis. The bulk unit cell c-vector is (0,0,4.17) Å.
The system has a noncolinear spin configuration.
When I add a 5Å vacuum the calculation converges without any negative rho.
However, as I increase the vacuum thickness the calculation still converges but negative rho develops.
I thought that having more vacuum is better, but I am seeing the opposite,  e.g for  vacuum=12Å
I have:
negative rho (up, down):  1.218E-05 2.046E-02
at the end of the calculation.

Also, I have lower energy for vacuum=5Å than for vacuum=10,12,14,16,18,20 Å

Many Thanks,

Marios Georgiou
School of Physics and Astronomy
University of Leeds

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