In Eq. ( ), 𝑎 In this work, 1-RDMs are constructed following measurements of parametrized quantum circuits (ansätze), representing the ground state of molecules of interest. Measurement of the 1-RDM scales as 𝑂(𝑛 $ ), rendering a density-based fidelity witness approach computationally efficient. We will return to discuss the sensitivity of 𝐷 13 to noise on quantum devices and how the outcome of calculations can be affected by enforcing physically motivated constraints on the 1-RDM.