convergence problem with transiesta
Dear all,
As a new user, I'm currently trying Siesta and Transiesta, which are really impressive and memory efficient by the way.
Nevertheless, I'm running into some problems when investigating systems with non-periodic left and right leads.
For the sake of simplicity, I'm looking at graphene, with a central region that is an atom less or greater than a conventional cell.
However, I'm running into convergence problem for the cases (1) and (3) discuss below.
Could you please help me regarding such problem ? which parameters to change to solve it ? my current guess concerns the contour parameters.
For the initial case, the subsequent atomic coordinates are :
AtomicCoordinat
%block AtomicCoordinat
0.000000000 0.00 0.0 1 # leadl
1.420281664 0.00 0.0 1
2.130422494 1.23 0.0 1
3.550704154 1.23 0.0 1
4.260844984 0.00 0.0 1
5.681126650 0.00 0.0 1
6.391267480 1.23 0.0 1
7.811549140 1.23 0.0 1
8.521689970 0.00 0.0 1 # device
9.941971637 0.00 0.0 1
10.65211246 1.23 0.0 1
12.07239412 1.23 0.0 1
12.78253495 0.00 0.0 1
14.20281662 0.00 0.0 1 # leadr
14.91295745 1.23 0.0 1
16.33323911 1.23 0.0 1
17.04337994 0.00 0.0 1
18.46366161 0.00 0.0 1
19.17380244 1.23 0.0 1
20.59408410 1.23 0.0 1
21.30422493 0.00 0.0 1
%endblock AtomicCoordinat
%block ChemicalSpecies
1 6 C.gga
%endblock ChemicalSpecies
The problem comes when I run the Transiesta calculation;
The methodology is the following :
1) If I put :
%block LatticeVectors
22.72450659 0.00 0.0
0.00000000 2.46 0.0
0.00000000 0.00 20.0
%endblock LatticeVectors
then it converges (wrongly I assume) to a large positive energy, which makes sense to me due to the additional states created at the interface on the non-periodic leads.
2) If i put :
%block LatticeVectors
54.1447882522 0.00 0.0
0.0000000000 2.46 0.0
0.0000000000 0.00 20.0
%endblock LatticeVectors
then it converges properly, with the Transiesta calculation energy being close to the Siesta one, which again makes sense to me as we get rid of those additional states
3) However, if I keep this supercell while adding H atoms at the edges as well as an additional cell as buffer, I'd assume to get a better convergence (or at least close) than for (2). Actually, it is not the case as the Transiesta energy is again positive, similarly to (1).
This means setting :
%block LatticeVectors
64.1447882522 0.00 0.0
0.0000000000 2.46 0.0
0.0000000000 0.00 20.0
%endblock LatticeVectors
AtomicCoordinat
%block AtomicCoordinat
24.6391550 0.00 0.0 2 # buffer
25.7391550 0.00 0.0 1
27.1594366 0.00 0.0 1
27.8695775 1.23 0.0 1
29.2898591 1.23 0.0 1
30.0000000 0.00 0.0 1 # lead l
31.4202816 0.00 0.0 1
32.1304224 1.23 0.0 1
33.5507041 1.23 0.0 1
34.2608449 0.00 0.0 1
35.6811266 0.00 0.0 1
36.3912674 1.23 0.0 1
37.8115491 1.23 0.0 1
38.5216899 0.00 0.0 1 # device
39.9419716 0.00 0.0 1
40.6521124 1.23 0.0 1
42.0723941 1.23 0.0 1
42.7825349 0.00 0.0 1
44.2028166 0.00 0.0 1 # lead r
44.9129574 1.23 0.0 1
46.3332391 1.23 0.0 1
47.0433799 0.00 0.0 1
48.4636616 0.00 0.0 1
49.1738024 1.23 0.0 1
50.5940841 1.23 0.0 1
51.3042249 0.00 0.0 1
52.7245065 0.00 0.0 1 # buffer
53.4346474 1.23 0.0 1
54.8549290 1.23 0.0 1
55.5650699 0.00 0.0 1
56.6650699 0.00 0.0 2
%endblock AtomicCoordinat
%block ChemicalSpecies
1 6 C.gga
2 1 H.gga
%endblock ChemicalSpecies
Question information
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- Samuel Dechamps
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