Validating variational quantum eigensolver (VQE) pipelines on realistic chemical systems is a critical stepping stone toward tackling classically intractable molecules. In this work, we report emulator-based validation of the VQE workflow proposed for the copper active site, executed on the LRZ Eviden Qaptiva emulator. A problem-tailored ADAPT-VQE with a full singles-doubles-triples (S+D+T) pool removes over 99% of the correlation error, reaching a stable plateau at 4.03 mEh relative to exact diagonalisation (148 selected operators). This establishes a >40x improvement over the hardware-efficient ansatz (HEA). Finally, we frame these emulator results as a robust baseline for upcoming physical quantum hardware runs on Euro-Q-Exa.