Orbital-Optimized Unitary Coupled Cluster for Indirect Nuclear Spin-Spin Coupling Constants within a Quantum Linear...

Area of Science:

• Quantum chemistry
• Computational spectroscopy
• Nuclear Magnetic Resonance (NMR)

Background:

• Indirect nuclear spin-spin coupling constants are crucial for interpreting NMR spectra.
• Accurate prediction of these constants requires sophisticated quantum chemical methods.
• Developing quantum computing-compatible methods is a key goal in computational chemistry.

Purpose of the Study:

• To present a quantum linear response (qLR) approach for calculating nuclear spin-spin coupling constants.
• To implement this approach using unitary coupled cluster (UCC) and orbital-optimized UCC (ooUCC) for quantum computing suitability.
• To assess the accuracy and impact of orbital optimization on coupling constant predictions.

Main Methods:

• Quantum linear response (qLR) theory applied within an active space framework.
• Unitary Coupled Cluster (UCC) and its orbital-optimized variant (ooUCC) ansatz.
• Comparison with established methods like CASCI, CASSCF, CCSD, and CC3.

Main Results:

• The qLR approach with UCC/ooUCC successfully computes spin-spin coupling constants.
• Results obtained are comparable to those from traditional classical methods.
• Orbital optimization in ooUCC significantly impacts the computed couplings, enhancing agreement with CCSD and CC3.

Conclusions:

• The qLR method with UCC/ooUCC is a viable approach for predicting NMR spin-spin coupling constants.
• Orbital response is a critical factor for achieving high accuracy in these predictions.
• The developed method shows promise for quantum computing applications in NMR spectroscopy.