Dear siesta users,
I am using Ni(111) electrodes in a transiesta calculation. For the electrodes,
I use a primitive surface unit cell and hence the electrode atomic positions
are is in the input file at the end of this post.
My question is how to choose the number of k-points in the transport direction
(z-direction) for both the electrodes and the scattering region. On the one
hand, I need to obtain well-converged density matrices for the semi-infinite
electrode, so I think I should use sufficient sampling points in the
z-direction for the electrode calculation. On the other hand, I should only
need one k-point along the transport direction for generating the electrode
surface green's function. For a the unit cell give in the input below, what
would be a wise choice for the monkhorst pack grid?
As for the scatterer, one k-point in the transport direction should be
sufficient, I suppose.
As I understand it the steps to be followed in a transiesta calculation are as
follows:
1- Use siesta to solve the K-S equations self consistently for the electrodes
and generate Hamiltonian and overlap matrices from which a surface green
function is constructed.
2- In a separate calculation, use SIESTA to solve the K-S equations self
consistently for the scattering region, again generating H and S matrices from
which a surface green function is constructed.
3- Use the resulting H & S matrices for obtains from step 1 and 2 to calculate
transmission used the Green's function formalism.
I understand that these in-plane k-point sampling must be identical for step 1
and 2 in order to form the coupling matrices at the interface between the
electrodes and the scatterer. Yet the sampling along z-dir can and should? be
different for electrode and scatterer. Right?
The electrode structure is given below and my choice of k-point sampling for
the electrode is:
%block kgrid_Monkhorst_Pack # Gamma centered grid
24 0 0 0.0
0 24 0 0.0
0 0 8 0.0
%endblock Kgrid_Monkhorst_Pack
----------------ELECTRODE
STRUCTURE------------------------------------------------------
NumberOfSpecies 1
NumberOfAtoms 3
%block ChemicalSpeciesLabel
1 28 Ni_lda
%endblock ChemicalSpeciesLabel
LatticeConstant 3.4860 Ang
%block LatticeVectors
0.707107 0.000000 0.000000
-0.353553 0.612372 0.000000
0.000000 0.000000 1.732051
%endblock LatticeVectors
AtomicCoordinatesFormat Fractional
%block AtomicCoordinatesAndAtomicSpecies
0.66666667 0.33333333 0.00000000 1 #C
0.33333333 0.66666667 0.33333333 1 #B
0.00000000 0.00000000 0.66666667 1 #A
%endblock AtomicCoordinatesAndAtomicSpecies
Thank you very much for your help,
Diana Otálvaro
[email protected]
Computational Material Science
MESA+ Institute for Nanotechnology
University of Twente
Carre 4049
Postbus 217
NL-7500 AE Enschede
tel: +31-53-489-2986
