Hi there,
I’m trying to calculate the phonon transport for through molecules between two Au-electrodes. Yet, I’ve struggled for a long time to get transmission that looks correct.
As a sanity check, I’ve calculated the transmission for a bare 4x4 slab with two small pyramids:
Only the two small pyramids are in the central region. The separation between the two tips is ~23Å.
I don’t expect much, if any, transmission for this system yet I see significant transmission at ~0eV.
The force constants of my electrodes have been calculated with these options:
TimeReversalSymmetry false
%block kgrid.MonkhorstPack
2 0 0 0.
0 2 0 0.
0 0 2 0.
%endblock
# This is the remaining default SIESTA options
PAO.BasisSize DZP
XC.functional GGA
XC.authors PBE
MeshCutoff 300.000000 Ry
SCF.DM.Tolerance 0.0001
# Mixing parameters:
SCF.Mixer.Weight 0.10
SCF.Mixer.History 10
DM.UseSaveDM true
MD.NumCGSteps 0
SaveHS T
Write.Forces True
I utilize the bloch expansion in the transmission calculation so the smallest unit of the electrode is:
18
sisl-version=1 cell= 2.88499567 0.00000000 0.00000000 0.00000000 4.99695908 0.00000000 0.00000000 0.00000000 21.20030188
Au 0.00000000 0.00000000 0.00000000
Au 1.44249783 2.49847954 0.00000000
Au 1.44249783 0.83282651 2.35558910
Au 0.00000000 3.33130605 2.35558910
Au 0.00000000 1.66565303 4.71117820
Au 1.44249783 4.16413256 4.71117820
Au 0.00000000 0.00000000 7.06676729
Au 1.44249783 2.49847954 7.06676729
Au 1.44249783 0.83282651 9.42235639
Au 0.00000000 3.33130605 9.42235639
Au 0.00000000 1.66565303 11.77794549
Au 1.44249783 4.16413256 11.77794549
Au 0.00000000 0.00000000 14.13353459
Au 1.44249783 2.49847954 14.13353459
Au 1.44249783 0.83282651 16.48912369
Au 0.00000000 3.33130605 16.48912369
Au 0.00000000 1.66565303 18.84471279
Au 1.44249783 4.16413256 18.84471279
The electrode is calculated with a supercell expansion of 5x3x2.
I’ve read this from the mailing list talking about the need for large electrodes, but I imagined that the ones I’ve used would be large enough?
I’ve also tried with a bigger surface (6x6, 8x8, 10x10), but that doesn’t seem to help.
Do I just need to bite the bullet of calculating an even deep electrode? And if so, why? I would think that 23Å of vacuum would not transmit any phonons?
I sincerely hope someone can assist me as I’m at my wits end