Drude-Lorentz Fit Version 1.1 Usage
- Load data that you want to fit:
- If you are using the provided Johnson-Christy data click the
Load button and select one of three files, the name of the
file should be visible next to the button:
- Gold - JCDataAu.dat
- Silver - JCDataAg.dat
- Copper - JCDataCu.dat
- If you want to use your own data you have to provide your
own data file with a suited format:
- The data file must be a table of 5 columns.
- First column is energy (frequency will also work).
- Second column is the refractive index (n).
- Third coulmn is the RMS error of the refractive index (if
not available use 1).
- Fourth coulmn is the absorption index (k).
- Fifth coulmn is the experimental error for absorption
index (if not available use 1).
- Adjust parameters:
- By default there is a Drude pole
included but this can be removed by unchecking the Drude
- Choose the maximum number of Lorentz poles L to be used. The
fit will increase L from 0 to this
number. For example, if L=3 is
selected as the maximum, then curves for L=0,1,2,3
will be calculated and shown on the figure.
- The slider for maximum energy E_max
will, by default, select the total number of data points to
fit. This can be adjusted to select fewer data points. Note that
E_min is always the lowest energy in
the data set and is not adjustable.
- By default the provided experimental errors are used,
uncheck the box if a constant error of unity should be used.
- The background epsilon can be fixed to a specific value is
needed, otherwise it will also be optimized.
- For the L=1
fit one can select to first use for each E_max
using random guesses or just for the maximum E_max.
- There are some control variables for
the zeta function to restrict the Lorentz poles to realistic
values, set any of the parameters to zero in order to remove
them from the final zeta function:
- Pushes away from imaginary axis (s1)
- stops the poles having frequencies with a negligible
real part and being similar to Drude poles.
- Pushes away from real axis (s2)
the poles having frequencies with a positive imaginary
part or very small imaginary part resulting in
- Pushes away from other poles (s3)
- stops poles overlapping each other.
- Prevent far energy poles (s4)
- stops the pole frequencies being too large in comparison
to the data energy range.
- If the refinement option is selected, start values from the L Lorentz poles are
additionally used for L-1
poles, for each L.
This can yield an improvement if the global minimum had not
yet been found while increasing L. This option can
be selected while a calculation still running.
- Once all the parameters have been chosen you can run the
program. Most options will become fixed at this point to keep
consistency. They will become modifiable again once the
calculation is complete. The calculation can be stopped at any
time, keeping as output the actual status.
- The smallest figure on the main panel
shows the imaginary part of the permittivity.
- The largest figure in the main
panel shows how the S-values are being calculated:
- L=0 (Drude only) will be calculated quickly due to
few parameters being optimized.
- L=1 will calculate using random guesses until the
cut-off criterion has been met (see paper Section IV B). All
minima found are shown in red until the taken as correct when
the lowest three minima found are within 10% relative value.
- L>1 does not use random guess values, but the
poles for L-1
plus one additional pole at E_max
(see paper for details) . Note
that after each L has been
calculated there is a 'smoothing function' which
improves S-valuas starting values the nearest neighbours
(calculation cannot be stopped here).
- The program only calculates for energy ranges were the
number of data values to be fitted exceeds the number of
- Once the calculation has completed the 'GRAPHS' button will
open a new panel to display the experimental and model
- There is a checkbox option to show the refractive and
absorption index instead. Select the desired L and click on the
slider to display results.
- The save button will save the current model data at the
experimental energies as modelFit.dat in the current
- After the calculation has finished the results are saved in
the current directory (view in excel or similar) in the
following output files:
- error.dat contains the S-values calculated up to the maximum
- paramNumPolesL.dat has a list of parameters for all
energy ranges for a specific L. There will be L+1 files
showing parameter lists for the respective number of Lorentz