In reality, binding energy is the mechanical energy required to disassemble a whole into separate parts. It should be measured against the element in its 'pure' form (for instance, O2 for oxygen). However, some software can give you cohesive energy (energy measured against the isolated atoms, or -cohesive energy ) and can call it as binding energy

thank you so much Dr Malyi for the response

The binding energy reported in DMol3 is to dissociate the molecule or crystal into atoms at infinite separation.