An entry in the COD is considered a duplicate of another entry, if all of the following conditions are met for both structures:

  • chemical compositions are the same: structures are considered as having the same chemical composition if any of the following conditions are met:

    • the values of the _chemical_formula_sum data item match identically;
    • the calculated summary formulae match identically;
    • the calculated unit cell formulae match identically;
  • cells are the same: cell parameters differ no more than 0.5 Å (lengths) and 1.2 degrees (angles);

  • conditions are the same: temperature, pressure and corresponding histories are the same (or are not known); the following data items are taken into consideration:

    • _cell_measurement_temperature
    • _cell_measurement_temperature_C
    • _diffrn_ambient_temperature
    • _diffrn_ambient_temperature_C
    • _diffrn_ambient_temperature_gt
    • _diffrn_ambient_temperature_lt
    • _pd_prep_temperature
    • _cell_measurement_pressure
    • _cell_measurement_pressure_gPa
    • _cell_wave_vectors_pressure_max
    • _cell_wave_vectors_pressure_min
    • _diffrn_ambient_pressure
    • _diffrn_ambient_pressure_esd
    • _diffrn_ambient_pressure_gPa
    • _diffrn_ambient_pressure_gt
    • _diffrn_ambient_pressure_lt
    • _exptl_crystal_pressure_history
    • _exptl_crystal_thermal_history
    • _pd_prep_pressure
  • compound source is the same: values of data item _chemical_compound_source are the same (or are not known);

  • bibliographies are the same (not checked for ?personal communication entries): DOIs or full bibliographies are the same (or are not known for both entries);

  • are not enantiomers or suboptimal of one another: values of data items _cod_enantiomer_of and _cod_related_optimal_struct are not known or do not specify the corresponding relation.

Deposition of duplicates of entries, already present in the COD, are not accepted. However, entries that are already in the COD and are later ruled out to be duplicates of other COD entries are not deleted, but marked with _cod_duplicate_entry CIF tag.