[DFTB-Plus-User] hexagonal lattice and choice of k point mesh

[Μανόλης Κλώντζας]

Dear Users,

i am trying to perform TBDFT calculations for periodic structures composed
by graphene layers covalently bonded with organic molecules. The lattice is
hexagonal (a=b, c, α=β=90, γ=120) and the length of the c axis is 5 to 8
times larger than the length of a, depending on the length of the organic
molecule (a=5 Angstrom, c= 22 Angstrom). I have used both even and odd
number of k points using the “SuperCellFolding” option in the corresponding
section of the input file. I noticed that the calculated Fermi energy can
be different depending on the k point mesh while the energies of the HOMO
and LUMO did not change. In most of these cases, the Fermi energy is
shifted at the edges of the valence or the conduction band. What can be the
source of these differences? I suspect that I do something wrong with the
selection of the k point mesh.



Thanks in advance for the respond,

Best regards,

Manos


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