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

• URL: http://arxiv.org/abs/2511.09730v1
• Date: Fri, 14 Nov 2025 01:06:28 GMT
• Title: Orbital-Optimized Unitary Coupled Cluster for Indirect Nuclear Spin-Spin Coupling Constants within a Quantum Linear Response Framework
• Authors: Juliane H. Fuglsbjerg, Peter Reinholdt, Erik Kjellgren, Phillip W. K. Jensen, Sonia Coriani, Jacob Kongsted, Stephan P. A. Sauer,
• Abstract summary: We present a quantum linear response (qLR) approach within an active-space framework for computing indirect nuclear spin-spin coupling constants.<n>We examine the role of orbital optimization and find that ooUCC affects the computed couplings markedly.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We present a quantum linear response (qLR) approach within an active-space framework for computing indirect nuclear spin-spin coupling constants, a key ingredient in NMR spectra predictions. The method employs the unitary coupled cluster (UCC) ansatz and its orbital-optimized variant (ooUCC), both suitable for quantum computing implementations, to evaluate spin-spin coupling constants via qLR. Test calculations on five small molecules are compared with CASCI, CASSCF, and conventional CCSD results. qLR with UCC/ooUCC yields spin-spin coupling constants comparable to classical methods. We further examine the role of orbital optimization and find that ooUCC markedly affects the computed couplings; orbital-optimized results show better agreement with CCSD. These findings indicate that orbital optimization is important for accurate NMR coupling predictions within quantum-computing-friendly correlated methods.

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