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grid{}
Specifications of the non-uniform rectangular grid.
These grid lines set the total device size, so at least two lines have to be
present for each relevant direction.
grid{
xgrid{ #
x position of the line [nm] #
x grid spacing adjacent to this line [nm]
line{ pos =
0
spacing = 0.5 } #
0.5 nm spacing at position 0
nm
line{ pos =
50
spacing = 0.1 } #
0.1 50
nm
line{ pos =
100
spacing = 0.5 } #
0.5 100
nm
}
ygrid{ #
[nm] #
y grid spacing adjacent to this line [nm]
(2D or 3D only)
line{ pos =
0
spacing = 0.5 } #
0.5 0
nm
line{ pos =
50
spacing = 0.1 } #
0.1 50
nm
line{ pos =
75
spacing = 0.1 } #
<== #
0.1 75
nm - Here, two grid spacings are defined for y=75 nm, i.e.
for y<75 nm a grid spacing of 0.1 nm
line{ pos =
75
spacing = 0.5 } #
<== #
0.5 75
nm - and for y>75 nm a grid spacing of 0.5 nm is used.
line{ pos =
100
spacing = 0.5 } #
0.5 100
nm
}
75
nm an abrupt change in grid spacing is enforced is a bit dangerous.
This can have impacts on numerical stability and numerical accurateness
as discretized equations are only approximations to the continuous equations
being solved.
zgrid{ #
[nm] #
z grid spacing adjacent to this line [nm]
(3D only)
line{ pos =
0
spacing = 0.5 } #
0.5 0
nm
line{ pos =
50
spacing = 0.1 } #
0.1 50
nm
line{ pos =
100
spacing = 0.5 } #
0.5 100
nm
}
spacing
adjacent to the specified grid lines.
If the grid is not equidistant, an exponential grid is generated. In this
case, the calculated spacing corresponds only approximately
to the specified spacing.
grid_x.dat, grid_y.dat, and grid_z.dat.
Especially for more complicate grid definitions or grid definitions employing variables, it is recommended to review
these files to make sure that the results match your expectations.
You can also use nextnanomat ==> Output
==> Show grid to visualize the grid lines.
Repeating grid lines
In the same way as regions (==> region{})
can be repeated, also grid lines can be repeated which might be useful for
multi-quantum wells, superlattices, Quantum Cascade Lasers, Bragg reflectors, etc.
Also, it is possible to make the number of repetitions a variable in a
corresponding template.
array{} copies
the line object located at pos
a few times, namely min times into the negative direction
and max times into the positive direction,
i.e. the loop runs from
-shift*min to
shift*max.
xgrid{
line{ pos =
11.0 spacing = 0.5
#
0.5
11.0
nm
array{
#
array, see
array_x{} in structure{}.
shift
=
10.0 #
10.0 nm (in units of [nm])
max
= 3 # shift 3
(=max) times (Here,
4 lines will be set: The original one specified at pos, and 3
shifted ones.)
# max =
0
min
= 2 } # 0)
repeat grid line in negative x direction 2
times
# min =
0
# 11.0 nm is repeated
2 (=min) times
into the negative direction and 3 (=max)
times into the positive direction,
# i.e. additional grid lines at
1.0 nm,
-9.0 nm and
21.0 nm,
31.0 nm,
41.0 nm will be set.
array2{ array{} } # (optional) For meaning of
array2{}, see array2_x{}
in structure{}.
}
}
line{}
are processed in the order of their occurrence in order to obtain a list of default grid lines.
Here, within each line{} definition, duplicate grid lines created by
array{} and
array2{}
are ignored.
After all line{} definitions have been processed, the list of default grid lines is ordered in ascending position
(but the order of doubled lines remains unchanged),
and intermediate grid lines are added as suggested by the respective grid spacings.
Note that array{} and
array2{} may accidentally cause doubled grid lines between different
line{} definitions.
In this case, resulting jumps in grid spacings may be nonobvious and should be checked in the output.
xgrid{
min_pos = 100.0
#
(optional)
nm
max_pos = 200.0
#
nm
line{ ... }
}
min_pos
and max_pos
(defaults are -Infinity and +Infinity), a (half-)range can be defined for each coordinate direction
within which
all grid lines to be used are located.
Grid lines located outside (e.g. due to a position defined by a formula or by a repetition) will be ignored.
Please note that specifying a (half-)range in itself does not specify a grid line for the respective range limit(s).
Similarly, there is no automatic insertion of grid lines as controlled by the respective spacings between a grid line
defined inside of a (half-)range and an adjacent grid line defined outside of the (half-)range.
Per default, all defined grid lines are used for the computation, with the boundaries of the simulation region being defined by the
smallest and largest
coordinate positions of all grid lines defined for a respective coordinate direction.
However, there are circumstances where structural features are partially or completely
outside of the simulation region,
and thus no grid lines are allowed for these structural features.
Here, in order to facilitate reuse of coordinate calculations between region definitions and grid definitions,
it is helpful to set min_pos
and max_pos
to the desired extent of the simulation region in order to prevent unwanted grid lines from being generated.
All grid line definitions from line{}
which fall outside of the interval [min_pos, max_pos] are ignored.
Thus, if the such defined interval is [100, 200], an individual line with pos = 250
would be ignored.
Similarly, when a line is repeated using
array{}
and/or array2{} multiple times, the line repetitions falling outside of the interval would be ignored.
For all nextnano versions newer than
2019-03-08, the periodic{} flag is specified within the
global{}
section and not within the grid{}
section any more.
periodic{
#
x = yes/no
#
no)
y = yes/no
#
no) (2D
or 3D only)
z = yes/no
#
no) (3D
only)
}
global{}
section.
}
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