Sample-based quantum diagonalization approach for open-shell transition-metal complexes in gas and implicit-solvent
Abstract
Open-shell 3d transition-metal complexes pose a stringent challenge for correlated electronic-structure methods because near-degenerate metal d orbitals give rise to competing spin states and oxidation-state-dependent charge transfer, while solvation can reshape the relative stability of the resulting electronic configurations. Building on prior demonstrations of open-shell sample-based quantum diagonalization (SQD) for light-atom systems and, separately, closed-shell SQD coupled to the integral-equation-formalism polarizable continuum model (IEF-PCM), we combine these capabilities through an open-shell SQD--IEF-PCM framework and apply it to the octahedrally coordinated [Co(H2O)5CO2]2+/3+ complex, spanning the Co(III) singlet and quintet and Co(II) doublet and quartet states along a metal--ligand dissociation coordinate. Using quantum samples collected on an IBM Heron processor and active spaces of up to 50 qubits, SQD closely reproduces coupled-cluster and heat-bath configuration-interaction benchmarks within the same active spaces in both gas phase and implicit solvent; for high-spin quintet [Co(H2O)5CO2]3+, it additionally resolves an avoided crossing associated with internal charge transfer that is absent in the corresponding singlet and in the lower oxidation state, while IEF-PCM suppresses this crossover by preferentially stabilizing the dissociation channel leading to neutral CO2. To our knowledge, this work provides the first hardware demonstration of SQD for an open-shell 3d transition-metal complex with discrete metal-centered d-orbital chemistry, and the first application of open-shell SQD in a dielectric continuum, establishing a quantum-centric framework for transition-metal chemistry in regimes where spin-state energetics, charge transfer, and environmental response are strongly coupled.
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BibTeX
@misc{david2026samplebased,
title = {{Sample-based quantum diagonalization approach for open-shell transition-metal complexes in gas and implicit-solvent}},
author = {David David and Vedangi Pathak and Marek Kowalik and Hamed Mohammadbagherpoor and Vincent Beltrani and Kara Maller and Niall Moroney and Phalgun Lolur},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2607.16389},
eprint = {2607.16389},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.16389},
}
RIS
TY - UNPB
TI - Sample-based quantum diagonalization approach for open-shell transition-metal complexes in gas and implicit-solvent
AU - David David
AU - Vedangi Pathak
AU - Marek Kowalik
AU - Hamed Mohammadbagherpoor
AU - Vincent Beltrani
AU - Kara Maller
AU - Niall Moroney
AU - Phalgun Lolur
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2607.16389
UR - https://arxiv.org/abs/2607.16389
AB - Open-shell 3d transition-metal complexes pose a stringent challenge for correlated electronic-structure methods because near-degenerate metal d orbitals give rise to competing spin states and oxidation-state-dependent charge transfer, while solvation can reshape the relative stability of the resulting electronic configurations. Building on prior demonstrations of open-shell sample-based quantum diagonalization (SQD) for light-atom systems and, separately, closed-shell SQD coupled to the integral-equation-formalism polarizable continuum model (IEF-PCM), we combine these capabilities through an open-shell SQD--IEF-PCM framework and apply it to the octahedrally coordinated [Co(H_2O)_5CO_2]^2+/3+ complex, spanning the Co(III) singlet and quintet and Co(II) doublet and quartet states along a metal--ligand dissociation coordinate. Using quantum samples collected on an IBM Heron processor and active spaces of up to 50 qubits, SQD closely reproduces coupled-cluster and heat-bath configuration-interaction benchmarks within the same active spaces in both gas phase and implicit solvent; for high-spin quintet [Co(H_2O)_5CO_2]^3+, it additionally resolves an avoided crossing associated with internal charge transfer that is absent in the corresponding singlet and in the lower oxidation state, while IEF-PCM suppresses this crossover by preferentially stabilizing the dissociation channel leading to neutral CO_2. To our knowledge, this work provides the first hardware demonstration of SQD for an open-shell 3d transition-metal complex with discrete metal-centered d-orbital chemistry, and the first application of open-shell SQD in a dielectric continuum, establishing a quantum-centric framework for transition-metal chemistry in regimes where spin-state energetics, charge transfer, and environmental response are strongly coupled.
ER -