EXPBEAMS

The EXPBEAMS file contains the experimental data (beam intensities vs. energy, without normalization) to be compared against. The TensErLEED Manager will look for an EXPBEAMS.csv file (with or without the .csv extension) at initialization, but can also run without it up to the search. Executing search or $R$ -factor calculations is only possible with an EXPBEAMS file as it requires experimental data to compare to.

Format

E, ( 1\| 0), ( 1\| 1), ( 1|-1)
73.00, 5.40259E+02,         NaN,         NaN
73.50, 4.91900E+02, 1.75857E+02,         NaN
74.00, 4.43576E+02, 1.59667E+02,         NaN
74.50, 3.98344E+02, 1.45197E+02,         NaN
75.00, 3.59160E+02, 1.32677E+02,         NaN
75.50, 3.28612E+02, 1.22006E+02,         NaN
 ...         ...          ...            ...

For backwards compatibility, old experimental beam files formatted as AUXEXPBEAMS can easily be transformed to the EXPBEAMS file format with the beams utility utility.

Note

The EXPBEAMS.csv file generated by the ViPErLEED ImageJ plug-ins contains some extra information in the header line that is not used while comparing to calculated beams. The information is kept for the possible interest of users. For each beam, the EXPBEAMS.csv file generated by the ViPErLEED ImageJ plug-ins reports a (positive or negative) integer index between square brackets. This is a progressive index that identifies symmetry-equivalent beams, and comes straight from the Pattern File that can be exported from the Graphical User Interface. Beams with the same absolute value of ‘group’ are symmetry-equivalent, beams with negative ‘group’ are extinct.

See here for an example (group indices are in the column group).

Warning

None of the EXPBEAMS.csv beams should have negative intensities. Negative intensities usually signal an inappropriate background subtraction. Beams with negative intensities will be offset to have minimum intensity equal to zero (issuing warnings of having done so). This behavior prevents errors while writing input files for the FORTRAN routines from TensErLEED. However, as this artificial offset affects the minima of the intensities, the $R$ factor may be impacted significantly. We strongly advise that the problematic beams are fixed or discarded by removing them from IVBEAMS. Consider improving background subtraction, or restricting the affected beams to the energy range where intensities are positive.

Warning

Gaps in the experimental beam set (i.e. a beam reappearing at higher energies) are currently not supported – neither supported in the spot tracker nor in viperleed.calc. We recommend using only the longest continuous part of any beam.