Aug 2026· Journal of the American Chemical Society· 1 citation· 108 references
Abstract
High-fidelity quantum chemical (QM) data sets that jointly resolve reaction thermochemistry, kinetics, and solvation at scale remain scarce, especially for radical chemistry. We introduce QuantumPioneer, an open-access reaction-centered QM database and workflow for small organic molecules, focused on peroxyl-mediated hydrogen atom transfer (HAT) and the corresponding homolytic bond dissociation reactions. QuantumPioneer contains 348,258 species (2–21 heavy atoms), 167,237 validated HAT transition states (TS) with corresponding reaction energies and homolytic bond dissociation energies (BDEs), and over 100 million COSMO-RS solvation free energies(ΔGsolv*) and enthalpies (ΔHsolv*) across 295 solvents. The workflow uses ωB97X-D/def2-SVP geometries, DLPNO–CCSD(T)-F12d/cc-pVTZ-F12 single-point energies, empirical thermochemical corrections, transition-state theory, and COSMO-RS BP-TZVPD-FINE solvation in a single high-throughput pipeline. Our benchmarks show reliable accuracy, with mean absolute errors (MAEs) compared to experimental and high-level QM reference data of 0.82 kcal/mol for gas-phase enthalpies of formation, 1.60 kcal/mol for C–H BDEs, 1.45 kcal/mol for HAT barriers, and 0.57 kcal/mol for ΔGsolv* values. We demonstrate two predictive applications. First, we show that combining BDE and HAT-barrier models identifies experimentally observed oxidative degradation sites in drug-like molecules with a 91% top-5 hit rate and 82% site-level recall. Second, we show that a QM-parametrized Abraham model enables rapid solvation energy estimates at near-COSMO-RS accuracy within its training domain, reproducing computed ΔGsolv* and ΔHsolv* values with MAEs of 0.16 and 0.18 kcal/mol, respectively, though performance on experimental ΔGsolv*values for unseen solutes was worse, with an MAE of 1.32 kcal/mol. This work provides a scalable template for other reaction families, unifying equilibrium species, validated TS, thermochemistry, kinetics, and solvation into one workflow.
Open-shell $3d$ transition-metal complexes challenge electronic-structure methods because competing spin states, charge transfer, and solvation jointly determine their energetics. Here, we combine sample-based quantum diagonalization (SQD) with the integral-equation-formalism polarizable continuum model (IEF-PCM), extending SQD to correlated open-shell transition-metal systems in a dielectric environment. We investigate the octahedrally coordinated $\mathrm{[Co(H_2O)_5CO_2]^{2+/3+}}$ complex across two oxidation states, four spin multiplicities, and a metal-ligand dissociation coordinate. We study the Co(III) singlet and quintet states and the Co(II) doublet and quartet states, incorporating open-shell references into SQD-IEF-PCM through an outer self-consistent reaction-field loop. Using samples collected on an IBM Heron quantum processor and active spaces of up to 50 qubits, SQD reproduces coupled-cluster and heat-bath configuration-interaction benchmarks within the same active space in the gas phase and implicit solvent, with a largest observed deviation below 9 $mE_h$. Along the dissociation coordinate of high-spin quintet $\mathrm{[Co(H_2O)_5CO_2]^{3+}}$, SQD resolves an avoided crossing caused by internal charge transfer; this feature is absent in the singlet and the lower oxidation state of the complex. Relative to the gas phase, implicit solvation stabilizes for the quintet state the neutral CO$_2$ dissociation and suppresses the avoided-crossing feature. To our knowledge, this is the first hardware demonstration of SQD for an open-shell $3d$ transition-metal complex in gas phase and implict solvent. These results establish SQD as a robust quantum-centric approach for transition-metal chemistry where spin state ordering, charge transfer, and environmental effects are strongly intertwined.
David R. David, Vedangi Pathak, Marek Kowalik et al.· 0 citations
We introduce population-transfer dynamics as a practical validation observable for active-space-derived reduced Hamiltonians in multistate reaction-center chemistry. Using a cytochrome P450-inspired Fe-complex model, we construct a reaction-coordinate-dependent effective Hamiltonian from state-averaged complete active-space self-consistent field (SA-CASSCF) calculations, map it to a quantum-circuit representation suitable for current hardware, and propagate dynamics from the reactant-side ground state. The reduced Hamiltonian reproduces the SA-CASSCF reference with an RMS deviation of 0.030 eV and a maximum absolute deviation of 0.143 eV. As a dynamics-based diagnostic, the product-manifold population p_P(t) identifies a pronounced near-degeneracy region around x = 0.3, where state mixing is strongest. Classical exact time evolution yields a product population of 0.488 at x = 0.3 after 10 fs, compared with 7.26 x 10^-2 at x = 0.2 and 5.90 x 10^-3 at x = 0.0. To enable execution on current trapped-ion hardware, we examine the trade-off between dynamical fidelity and circuit resources through coupling pruning and first-order Trotterization. A coupling cutoff of 0.02 eV reduces the non-zero coupling set from 32 to 7 while preserving the dominant transfer pathways, and M = 30 provides the best practical operating point. Finally, we demonstrate the workflow on Quantinuum's trapped-ion quantum computer Reimei. The hardware reproduces the key reaction-coordinate trend identified by the classical model, including the maximum at x = 0.3, where the measured product population is 0.42 on hardware and 0.43 on the matched emulator. This work establishes a dynamics-based framework for assessing active-space-derived reduced Hamiltonians and demonstrates chemically interpretable multistate electronic dynamics on current trapped-ion hardware.
Shintaro Maekawa, Takao Otsuka, Riku Masui et al.· 0 citations
Proton-coupled electron transfer (PCET) mediated by hydroquinone and related molecules is key to natural and artificial energy conversion. The reactivity of these molecules depends on their bond dissociation free energy (BDFE), but studying the relationship between structure and thermochemistry across this chemical space has been limited by challenging experimental setup and high computational expense. Here, we present the first use of the AIMNet2 neural network potential to calculate average BDFE (BDFEavg) values for the 2H+/2e− dehydrogenation of about 200 000 hydroquinone-like compounds, including vicinal diamines, diols, and dithiols. Benchmarking against DFT calculations for 168 substituted ortho-phenylenediamines (opda) shows good agreement (R2 ∼ 0.84). Our analysis finds that the BDFEavg of diamines ranges from 50 to 80 kcal mol−1 and can be systematically tuned by modifying the backbone and N-substitution: electron-withdrawing groups raise BDFEavg by up to 15 kcal mol−1, while lower aromaticity in furan and thiophene backbones decreases BDFEavg by approximately 10 kcal mol−1 compared to the phenyl systems (∼65 kcal mol−1). Validation through cyclic voltammetry and reactivity studies with quinone oxidants for selected compounds supports the computational results. This extensive thermochemical database and a web-based prediction tool developed as a result of this work will offer valuable resources for designing PCET reagents for catalysis, energy storage, and biomedical uses.
Rajdeep Sarma, Yiwen Wang, David D Hebert et al.· Chemical Science· 0 citations
Nuclear quantum effects (NQEs) are often central to a predictive understanding of chemical reactions and rates. While their incorporation in gas-phase reactions is well established, studies involving condensed matter often neglect or approximate such effects. To clarify the role of NQEs in multistep, multimolecular reactions in a molecular crystal, we compare atomistic simulations of the thermal decomposition of the energetic material TATB using the path integral-based thermostatted ring polymer molecular dynamics (TRPMD), the more approximate quantum thermal bath (QTB), and classical MD (ClMD). TRPMD samples the quantum canonical distribution by representing each atom as a string of beads (replicas), while QTB uses a frequency-dependent thermostat to reproduce the Bose-Einstein distribution. We find that TRPMD results in faster chemical decomposition of the TATB crystal compared to ClMD, as the initial steps involve hydrogen transfer processes. Interestingly, some of the subsequent reactions (e.g., the formation of N2) occur on identical time scales. The TRPMD simulations also predict a reduction in overall activation energy by ∼8% as compared to the classical result. As observed in model systems and simple unimolecular gas-phase reactions, the QTB significantly overestimates quantum acceleration of chemical reactions and the reduction in activation energy. A comparison of the kinetic energy operator in TRPMD and the centroid dynamics provides insight into the physics behind the differences between the QTB and TRPMD results.
Jalen Macatangay, Alejandro Strachan· Journal of Physical Chemistr...· 0 citations
Excited-state intramolecular proton transfer (ESIPT) and subsequent photoisomerization in o-hydroxy Schiff bases are central to many photochromic and fluorescent applications, yet the interplay between proton transfer and torsional relaxation in the simplest member of this family remains poorly understood. Here, we present the first fully nonadiabatic multireference dynamics study of 2-(iminomethyl)phenol (IMP), the minimal o-hydroxy Schiff base, using ab initio multiple spawning on extended multistate complete active space second-order perturbation theory (XMS-CASPT2) potential energy surfaces. Our simulations show that ESIPT in IMP is barrierless and ultrafast, with an overall time scale of ∼14 fs, placing the molecule firmly in the ballistic-transfer regime. The subsequent S1 lifetime of ∼220 fs is controlled by torsion about the C–C–C–N dihedral, with nonadiabatic transitions occurring predominantly at intermediate dihedral angles of 60–80° on a torsionally broad CI seam. Time-resolved joint distributions further reveal that proton transfer and torsional motion are dynamically, as well as energetically, decoupled. These results establish IMP as a quantitative benchmark for ultrafast ESIPT dynamics and provide directly testable predictions for emerging time-resolved X-ray photoelectron spectroscopy experiments.
Arshad Mehmood· Journal of Physical Chemistr...· 0 citations
Understanding how hydration reshapes the structure and conformational flexibility of biomolecular ions is essential for connecting gas-phase spectroscopy to behavior in aqueous environments. Glycine, the simplest amino acid, exhibits rich microsolvation behavior, with competing intra- and intermolecular hydrogen-bonding motifs that evolve with hydration and temperature. Although cryogenic ion spectroscopy has provided detailed measurements of hydrated protonated glycine (GlyH+) clusters, interpreting these spectra and relating them to molecular hydration motifs remains challenging. Here, we develop a data-driven many-body potential energy function for GlyH+–H2O interactions and combine it with replica-exchange molecular dynamics to identify isomeric equilibria, and with temperature-elevated path-integral coarse-graining simulations to model GlyH+(H2O)n clusters, accounting for nuclear quantum effects. This framework captures many-body interactions with high-level ab initio accuracy and enables direct computation of infrared spectra for comparison with experiment. By applying an inverse spectral reconstruction of isomeric ensembles, we quantitatively decompose the experimental spectra into contributions from competing hydration motifs and extract their relative populations. Our results characterize the sequential formation of the first and second solvation shells, quantify the competition between intramolecular and water-mediated hydrogen bonds, and reveal temperature dependence and nuclear quantum effects. Overall, this study provides a transferable approach to understanding the hydration of biomolecular systems across scales, from gas-phase clusters to bulk aqueous solutions.
Zoe A. Solomon, R. Rashmi, Ruihan Zhou et al.· Journal of Physical Chemistr...· 0 citations
