Hi there,
I am trying to understand the ESM example with bc2 (metal-slab-metal)
distributed with QE 6.0 which consists of an Al(001) slab between two
electrodes, and at the same time I am trying to replicate the results of Otani
and Sugino in their paper (Phys. Rev. B, 73, 115407, 2006) which consists of an
Al/Si(111)/Al slab between two screening boundaries.
I have a few questions:
** 1. ** In the QE example the following cell params and atomic positions are
specified:
CELL_PARAMETERS bohr
10.82227686 0.00000000 0.00000000
0.00000000 10.82227686 0.00000000
0.00000000 0.00000000 22.67672253
ATOMIC_POSITIONS bohr
Al 0.00000000 0.00000000 0.00000000
Al 5.41113843 0.00000000 0.00000000
Al 0.00000000 5.41113843 0.00000000
Al 5.41113843 5.41113843 0.00000000
My understanding is that the cell will repeat without overlapping atoms along X
and Y. What I'm not clear on is why the 3rd lattice vector is so large?
The parameter 'esm_w' defaults to zero and is not specified in the example, so
does this large value mean that there is a region of vacuum? Or does it just
repeat the atoms such that in the Z-direction there are 5 Al layers? I'm
guessing that this 3rd cell parameter Z-value corresponds to L_z, which in the
paper corresponds to z_0?
** 2. ** I have reproduced the 'surface unit cell' from Otani/Sugino's paper
using VESTA.
My concern here is with the correct repetition of atoms in X and Y, and what
exactly happens with the Z direction. I realize I must first rotate the unit
cell such that the repeated Al atoms lie perpendicular to the Z Cartesian axis
which I have not done yet.
I have tested the repetition of this cell within VESTA along vectors
perpendicular to the Al plane. So my most important question is: if the height
of the cell along Z is ~14.4281 Angstrom (measured from Al center plane), then
the third 'CELL_PARAMETERS' entry (after rotation) should be this value exactly
+ the 'decay length' of the wavefunction in Z? Then the parameter 'esm_w' is
used to set z_1 from the paper I suppose?
I will generate an xyz file of the surface cell, but if I repeat by 3.816 A
along a surface lattice vector, it is a matter of just deleting the entries
that cause an overlap of the atoms I suppose?
Thank you for your time and sorry for the very long email,
Kindest regards,
Louis
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