Yambo Community Forum

Hi Developers,
I am trying to plot the exciton and have a question about the definition of the origin in these plots. If i want to look at the exciton distribution with the hole fixed in the center of a 5x5x5 supercell, I would set:

% Cells
5 | 5 | 5 | # Number of cell repetitions (even or 1)
%
% Hole
2.500 | 2.500 | 2.500 | # [cc] Hole position in unit cell

or would I set:

% Cells
5 | 5 | 5 | # Number of cell repetitions (even or 1)
%
% Hole
0.000 | 0.000 | 0.0000 | # [cc] Hole position in unit cell

I am not sure how the origin is defined. Is it at the corner of a big cube or does Yambo automatically put it at the center of any supercell? I think it is the corner of the big cube, looking at the atom positions in the .xsf file, but I am not sure.

Thank you,
Marc Dvorak

Dear Marc,
if you set the hole position in the center of your unit cell,
then yambo will be place it in the center of the big cube.

If you set 5,5,5 in the cell repetition , you are constructing a big grid
with your cell repeated 5 time in space.The hole position have to be defined
inside the unit cell.

Hope it helps,
Daniele

I also have a doubt about the hole position. For my calculation on a 2D layered structure, the cell_parameters in input file of pw.x is as followed:
CELL_PARAMETERS
8.416824779 -4.36997605 0
-0.423902116 9.474172103 0
0 0 28.34588984

in the output file of pw.x, the lattice axes is showed in the following:
crystal axes: (cart. coord. in units of alat)
a(1) = ( 0.887509 -0.460790 0.000000 )
a(2) = ( -0.044698 0.999001 0.000000 )
a(3) = ( 0.000000 0.000000 2.988922 )

reciprocal axes: (cart. coord. in units 2 pi/alat)
b(1) = ( 1.153546 0.051613 0.000000 )
b(2) = ( 0.532075 1.024807 0.000000 )
b(3) = ( 0.000000 0.000000 0.334569 )

well, after calculation of yambo, I what to get the cube file of an exciton state by fixed the hole in the center of the lattice by set the hole parameter in ypp.in as followed :
% Hole
0.50 | 0.50 | 0.50 | # [cc] Hole position in unit cell
%

however, the obtained hole site is not at the center of lattice but close to bottom of the lattice. I see the position in the in the end of l_stderr, that is :

# | % Cells
# | 7 | 7 | 1 | # Number of cell repetitions in each direction (odd or 1)
# | %
# | % Hole
# | 24.35722 | 16.04150 | 0.47243 | # [cc] Hole position in unit cell
# | %

why? and how to set in ypp.in to ensure the position what I want, such the center of the lattice?? Thank u in advance.

Dear Dr. Zhou Liu-Jiang,
This: will not put the hole in the middle of the cell, you have to specify the center in cartesian coordinate.

Best,

Daniele