Dear Louis, Thank you for using the ESM. The figure 1 in the paper shows how does the unit cell place in the z-direction. As you see, we need to put enough vacuum region on both sides of a slab. Accordingly, the 3rd cell parameter (Lz) becomes large. The z0 is not equal to Lz but equal to Lz/2.
There are some example calculations in ESM_examle directory. I recommend you to have a look at the Aluminum (001) slab calculations with various boundary conditions. Best regards, Minoru -------------------------------------------------------------------------------------------------------- Minoru Otani National Institute of Advanced Industrial Science and Technology Research Centre for Computational Design of Advanced Functional Materials email : [email protected] <mailto:[email protected]> --------------------------------------------------------------------------------------------------------- > On Feb 23, 2017, at 21:42, Louis Fry-Bouriaux <[email protected]> wrote: > > 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 > > _______________________________________________ > Pw_forum mailing list > [email protected] <mailto:[email protected]> > http://pwscf.org/mailman/listinfo/pw_forum > <http://pwscf.org/mailman/listinfo/pw_forum>
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