Deltas
Delta directories Deltas_XYZ and archives Deltas_XYZ.zip use the same Tensor index XYZ as the Tensor files. In fact, the index XYZ of a Deltas_XYZ.zip archive indicates that it was ** **created based on the Tensors with the same index, Tensors_XYZ.zip. Delta files are named using the pattern ‘DEL_N_El_k’, where N is the number of the atom (same numbering as in POSCAR), El is the chemical element being addressed by this Delta file (may differ from POSCAR element through ELEMENT_MIX), and k is a running index to distinguish multiple Delta files generated for the same atom and element (see below).
When a delta-amplitudes calculation starts and a Deltas_XYZ folder or Deltas_XYZ.zip archive already exist for the given Tensors_XYZ, ViPErLEED will read the previous Delta files to check whether they match the requested parameter variations. New Delta files will only be calculated if no file with the requested set of variations exists yet. If this is the case, the old Delta file will be kept nevertheless, and the index k will simply increment by 1 to distinguish the files. Therefore, several Delta files can accumulate for each atom if consecutive searches are performed, especially when searches are looped.
As with the Tensors, at the end of the calculation, the directory Deltas_XYZ is packed into an archive Deltas_XYZ.zip, which is moved into the ‘Deltas’ directory.