Lokhande RA, de Moura CEV, Gaikwad PB
… +1 more, Miranda-Quintana RA
J Phys Chem A
· 2026 May · PMID 42118961
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Following the work of Kossoski et al. on hierarchy CI (hCI) we propose an extended way of partitioning the Hilbert space by combining the excitation and the seniority sectors in a more general way. We define the hierarch...Following the work of Kossoski et al. on hierarchy CI (hCI) we propose an extended way of partitioning the Hilbert space by combining the excitation and the seniority sectors in a more general way. We define the hierarchy parameter, , involving two "weights" (α values), measuring the importance of excitation () and seniority () contributions to the wave function according to = α + α. This formulation generates alternative orderings of the excitation-seniority lattice and enables a systematic examination of how different balances between excitation and seniority influence correlation recovery. Four partitions are considered: positive slope diagonals (PSDs), which is equivalent to the original hCI scheme; negative slope diagonals (NSD); vertical chess horse (VCH); and horizontal chess horse (HCH). These partitions are evaluated for the BeH and for the cubic and linear H dissociation. These results show that the efficiency of a partition depends on the specific excitation-seniority sectors it includes at a given number of determinants. For BeH, the PSD/hCI hierarchical ordering ( = 2) incorporates the dominant low-seniority configurations most effectively and reaches near-CISDT quality with compact expansions compared to other partition schemes. For the H systems, NSD and HCH recover static correlation more rapidly in the dissociation regime, whereas VCH remains inefficient across all determinant counts. The present results, obtained in the STO-6G basis for small benchmark systems, are intended as a controlled methodological study of determinant ordering strategies rather than a comprehensive performance assessment. The ehCI framework provides a practical way to analyze how excitation and seniority interact and to design compact CI expansions.
Duda DP, Sprouse S, Hu Y
… +2 more, Wiedner ES, Dixon DA
J Phys Chem A
· 2026 May · PMID 42118665
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The properties of the fundamental hydrogen species, proton (H), hydrogen atom (H), and hydride anion (H) are critical to a vast range of chemical processes, yet their thermodynamic properties in nonaqueous solvents are n...The properties of the fundamental hydrogen species, proton (H), hydrogen atom (H), and hydride anion (H) are critical to a vast range of chemical processes, yet their thermodynamic properties in nonaqueous solvents are not well established. A hybrid supermolecule-continuum approach is used to predict the Gibbs free energies of solvation (Δ°) and standard redox potentials (°) for the 2H/H and H/H couples in acetonitrile (MeCN) and tetrahydrofuran (THF) following the approach previously used for water. Gas phase and solution phase structures were optimized with ωB97X-D/aug-cc-pVTZ. Solvation was treated with the SMD self-consistent reaction field model, and CCSD(T)/aug-cc-pVTZ gas phase calculations were used as a benchmark for method sensitivity. For H, the Δ° values are predicted to be -258.7 kcal/mol in MeCN and -259.2 kcal/mol in THF. The standard redox potentials for the 2H/H couple are +0.21 V (±0.1 V) in MeCN and +0.18 V (±0.15 V) in THF relative to the aqueous SHE (° = 4.28 V on the absolute scale), consistent with the available experimental data. The Δ° for H is predicted to be -76.9 kcal/mol in MeCN and -67.8 kcal/mol in THF, and for H, Δ° is predicted to be 2.1 kcal/mol in both MeCN and THF. These solvation energies yield calculated redox potentials for the H/H couple of -0.12 V (±0.3 V) in MeCN and -0.52 V (±0.1 V) in THF relative to the aqueous SHE. H solvation is near thermoneutral in both solvents. The p(H) is predicted to be 43.0 in MeCN and 49.3 in THF. The proton-coupled electron transfer (PCET) accounting term was evaluated on the ferrocene scale and deviates from the reported literature values by 7.5 kcal/mol in MeCN and 5 kcal/mol in THF. These results establish an internally consistent thermodynamic framework for hydrogen redox chemistry in MeCN and THF and improve consistency across °, Δ°, p, and .
J Phys Chem A
· 2026 May · PMID 42108606
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Time-resolved spectroscopy is a widely used tool for the investigation of physical and chemical processes. Analysis of the results is often challenging due to the inherent complexity of the data, encoding the chemical na...Time-resolved spectroscopy is a widely used tool for the investigation of physical and chemical processes. Analysis of the results is often challenging due to the inherent complexity of the data, encoding the chemical nature and time evolution of multiple species involved in the reaction. Many existing analytical methods are unsatisfactory as they introduce bias by relying on unjustified mathematical or mechanistic assumptions about the studied process. Here, we introduce a generalized analytical strategy based on non-negative matrix factorization. The methodology builds on a bottom-up model-free approach, in which physically grounded mathematical constraints can be introduced by active choice, allowing for an unbiased analysis of complex time series of spectroscopic data. The strength of this strategy is demonstrated by successful deconvolution of synthetic data mimicking different types of chemical reactions and typical challenges encountered in time-resolved Raman spectroscopy.
J Phys Chem A
· 2026 May · PMID 42102321
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Multiconfigurational short-range density functional theory (MC-srDFT) rigorously combines ground-state wave function theory with DFT. Unlike single-reference range-separated hybrid functionals, MC-srDFT has lacked theore...Multiconfigurational short-range density functional theory (MC-srDFT) rigorously combines ground-state wave function theory with DFT. Unlike single-reference range-separated hybrid functionals, MC-srDFT has lacked theoretically grounded protocols for choosing the system-specific range-separation parameter. To address this problem, we introduce an optimal-tuning scheme based on enforcing the correct exponential decay of the electron density. We show that the range-separation parameter can be determined from the ionization potential given by the smallest-magnitude eigenvalue of the Extended Koopmans' Theorem matrix constructed for the model Hamiltonian. We validate this approach for static and dynamic dipole polarizabilities of ground-state molecular systems using MC-srDFT within both full linear response and its extended random phase approximation (ERPA) variant. Optimal tuning substantially improves polarizabilities relative to the commonly used universal μ = 0.4 bohr parameter.
J Phys Chem A
· 2026 May · PMID 42099131
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Ligand-stabilized gold nanoclusters have raised significant interest due to great advances in their atom-precise design for a range of functionalities for catalysis, optoelectronic applications, bioimaging, and nanomedic...Ligand-stabilized gold nanoclusters have raised significant interest due to great advances in their atom-precise design for a range of functionalities for catalysis, optoelectronic applications, bioimaging, and nanomedicine. Theory and computational investigations can greatly help to understand the effects from clusters' environment to their electronic structure and optical excitations. Here, we have performed a systematic density functional theory study on the impact of large counterions on the electronic structure of small water-soluble gold (Au) clusters. We show that counterions not only stabilize cluster isomers as previously shown [Chem 2021, 7, 2227-2244] but also modulate excitation energies and redistribute oscillator and rotatory strengths among dipole-allowed transitions, significantly altering the photophysical behavior of the nanoclusters. These findings help to understand the photophysics of clusters in realistic solution-phase conditions advancing further design efforts for applications.
Khemissi S, Tiu CA, Kleiner I
… +3 more, Nguyen HVL, Crabtree KN, Hernandez-Castillo AO
J Phys Chem A
· 2026 May · PMID 42095403
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We report a high-resolution rotational study of -methylmaleimide and -methylsuccinimide using a molecular jet K-band Chirped Pulse Fourier-Transform MicroWave (CP-FTMW) spectrometer and two resonator-based FTMW instrumen...We report a high-resolution rotational study of -methylmaleimide and -methylsuccinimide using a molecular jet K-band Chirped Pulse Fourier-Transform MicroWave (CP-FTMW) spectrometer and two resonator-based FTMW instruments (Passage And Resonance In Synergy─PARIS and K-band "small cavity"). In both molecules, the methyl group undergoes facile internal rotation, splitting each rotational transition into the = 0 and = 1 torsional species. For -methylmaleimide, 672 hyperfine-resolved transitions were assigned from the PARIS (2-20 GHz) and "small cavity" data. A global fit using the program yielded an rms deviation of 89.1 kHz, and separate fits of the two torsional species confirmed the correctness of the assignment. The program improved the rms deviation to 4.5 kHz, consistent with the measurement accuracy. For -methylsuccinimide, 260 transitions were assigned from the K-band CP-FTMW spectra with a measurement accuracy of 25 kHz. The data were fitted first with the program to an rms deviation of 32.7 kHz, and then with the program, which reduced this value to 24.9 kHz. The torsional barriers were determined to be 20.2364(16) cm for -methylmaleimide and 25.833(11) cm for -methylsuccinimide. These values are significantly lower than that of -methylpyrrole (67.8 cm), suggesting that the two adjacent carbonyl substituents enhance the sensitivity of the methyl rotor to the local C electronic environment, thereby lowering the torsional barrier.
Gupta V, Anand R, Park IK
… +2 more, Brette F, Lee G
J Phys Chem A
· 2026 May · PMID 42095274
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Extreme ultraviolet (EUV) photoresist design involves a careful trade-off between maximizing absorption of highly energetic EUV photons (92 eV) and controlling electron-hole-induced chemical pathways driven by low-energy...Extreme ultraviolet (EUV) photoresist design involves a careful trade-off between maximizing absorption of highly energetic EUV photons (92 eV) and controlling electron-hole-induced chemical pathways driven by low-energy electrons (<20 eV). Using first-principles calculations, including density functional theory (DFT) and time-dependent DFT for optical properties, we systematically investigated the effects of halogen and halomethyl substitution on the electronic structure and electron-hole-induced chemistry for potential application in EUV photoresists. Iodine substitution promotes radical generation via an exothermic process along a dissociative electron attachment pathway and increases the intensity of the electron energy loss function and EUV absorption relative to fluorine, chlorine, and bromine. These results establish iodine as the most effective substituent for improving cross-linking efficiency and photon absorption and provide a first-principles framework for guiding the rational design of halogenated EUV photoresist materials.
J Phys Chem A
· 2026 May · PMID 42090403
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Accurate prediction of NMR chemical shifts for large biomolecules remains a major challenge due to the steep scaling of quantum-mechanical (QM) models with system size. Our group has developed a systematic fragmentation-...Accurate prediction of NMR chemical shifts for large biomolecules remains a major challenge due to the steep scaling of quantum-mechanical (QM) models with system size. Our group has developed a systematic fragmentation-based approach known as molecules-in-molecules (MIM) that is applicable for large biomolecular systems and can calculate their NMR spectra accurately. Here, we developed a hybrid fragmentation-based machine learning framework (MIM-ML) for predicting H and C NMR chemical shifts of large peptides. Low-cost single-layer MIM1-based DFT calculations with a microsolvation model were employed to generate the training data. For ML training, physics-based structural and electronic features were incorporated and derived from cost-efficient extended tight-binding (xTB) calculations. Our trained XGBR model using a relatively small amount of data (1406 for H and 837 for C) achieved mean absolute deviations (MADs) of 0.33 ppm for H and 2.91 ppm for C against experimental data for a test data set of large peptides. Furthermore, training the ML model directly on experimental chemical shifts produced results consistent with those of the DFT-trained model, indicating independence from the source of training data and a strong correlation between DFT-computed and experimental values. Overall, our developed ML model can be applied for the accurate prediction of the NMR chemical shifts for unknown large peptides.
James Pope T, Li B, Junkawitsch H
… +2 more, Bande A, James Penfold T
J Phys Chem A
· 2026 May · PMID 42087718
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X-ray spectroscopy provides sensitive, element-specific insight into local geometric and electronic structures, but predictive first-principles simulations can be computationally expensive for large and chemically divers...X-ray spectroscopy provides sensitive, element-specific insight into local geometric and electronic structures, but predictive first-principles simulations can be computationally expensive for large and chemically diverse molecular systems. Recent machine-learning approaches have shown promise in accelerating structure-to-spectrum prediction; however, most directly regress discretized spectral intensities and rely on hand-crafted geometric descriptors centered on the absorbing atom. Herein, we introduce a machine learning framework that encodes a detailed, environment-aware representation of the nuclear structure beyond the absorbing site. The model combines these descriptors with a physically motivated, multiscale Gaussian spectral basis whose coefficients are obtained via ridge projection, enforcing smoothness and spectral consistency. To further enhance robustness across chemical and conformational diversity, we employ a multiscale structural similarity loss that couples geometric and spectral resolution. This integrated approach yields accurate and transferable predictions across a wide range of molecular geometries and chemical environments while maintaining physical interpretability. The proposed framework establishes a physically structured and scalable route to machine-learned X-ray spectroscopy.
J Phys Chem A
· 2026 May · PMID 42086221
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We have used high-level quantum-chemistry methods to obtain the heat of formation (HOF) for a set of 539 organophosphorus species in the NIST database, for which reported values are not available. Machine learning is the...We have used high-level quantum-chemistry methods to obtain the heat of formation (HOF) for a set of 539 organophosphorus species in the NIST database, for which reported values are not available. Machine learning is then used to divide the HOFs into their atomic contributions. We find that the σ-electron-withdrawing CF group stabilizes the bonded phosphorus, while triple-bonded substituents tend to be thermochemically destabilizing. The atomic contributions are also shown to be useful for rationalizing reactivity, notably when thermochemical stability does not reflect chemical inertness. Furthermore, we have revised the optimal atomic values used for determining the HOFs by atomization with more economical methods and parametrized them for additional low-cost protocols. In particular, the combination of ωB97M-V and a revised vDZP basis set emerges as a good balance between cost and performance, making it suitable for obtaining an extensive set of HOF data with good statistical accuracy.
J Phys Chem A
· 2026 May · PMID 42085687
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Composite recipes based on ground-state coupled cluster methods can be used to calculate thermochemically relevant quantities such as heats of formation and ionization potentials to within 1 kJ/mol of experimental values...Composite recipes based on ground-state coupled cluster methods can be used to calculate thermochemically relevant quantities such as heats of formation and ionization potentials to within 1 kJ/mol of experimental values. Achieving this level of accuracy with composite recipes typically requires inclusion of electron correlation of up to quadruple excitations. In this study, composite recipes based on the equation of motion coupled cluster theory (EOM-CC) have been designed to calculate electronic excitation energies of cations and ionization potentials (IP) of closed-shell molecules. The adiabatic ionization energies were calculated using two different recipes, and the results were compared to experimental values. With the more rigorous recipe, predictions of excitation and ionization energies were consistently within subchemical accuracy, with the ionization energies predicted with a mean absolute error (MAE) of 25 cm. An alternative recipe, designed to be more affordable, was applied to calculate IPs for a set of 16 molecules; it predicted ionization energies with an MAE of 132 cm. The level of electron correlation required in these recipes to reach subchemical accuracy is indicative of the slower convergence of EOM-CC to the full configuration interaction limit compared to ground-state CC methods.
J Phys Chem A
· 2026 May · PMID 42084910
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Aromaticity is deeply rooted in organic chemistry, underpinning the electronic structure, stability, and reactivity of planar conjugated rings. While all-metal aromaticity in Al, Ga, and In has been reported, neutral M (...Aromaticity is deeply rooted in organic chemistry, underpinning the electronic structure, stability, and reactivity of planar conjugated rings. While all-metal aromaticity in Al, Ga, and In has been reported, neutral M (M = B-In) rings have attained limited attention. Herein, we report a unique feature of the neutral bare Al ring, which possesses a very rare σ-σ diradical character, whereas the other M rings have mixed σ-π diradical character. The present study clearly indicates that like the Al ring, neutral Al rings are also double (σ + π) aromatic, while Ga and In rings are σ-aromatic.
J Phys Chem A
· 2026 May · PMID 42084354
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The Cambridge Structural Database (CSD) was searched for crystals containing both tellurium(II) and iodine, revealing ten molecular crystals featuring distinct two-molecule aggregates encompassing Te···I interactions. Th...The Cambridge Structural Database (CSD) was searched for crystals containing both tellurium(II) and iodine, revealing ten molecular crystals featuring distinct two-molecule aggregates encompassing Te···I interactions. These supramolecular assemblies were classified into three categories based on their geometric characteristics: halogen bonds (HaB), chalcogen bonds (ChB), and Type I interactions. A systematic structural comparison with lighter congeners (substituting Te with Se, S, and I with Br, Cl, and F) highlighted the exclusive propensity of tellurium and iodine to form these specific motifs, often with limited isostructurality across the series. To provide deeper insight into the nature of these noncovalent interactions, Density Functional Theory (DFT) calculations (PBE0-D3/def2-TZVP) were conducted on five representative systems. The computational results, including Molecular Electrostatic Potential (MEP) surfaces, QTAIM, and NBO analyses, revealed that the supramolecular organization is governed by a delicate interplay between the nature of intermolecular Te···I contacts and additional Te···N, O, S, and Te contacts, intramolecular or external, which are classified as ChBs exclusively. The energetic analysis demonstrated that while some aggregates are driven by robust HaBs, others rely on the cooperative effects of weaker ChBs and auxiliary interactions, with substantial orbital charge transfer contributions confirmed by NBO analysis.
Bartashevich E, Regel R, Yushina I
… +1 more, Tsirelson V
J Phys Chem A
· 2026 May · PMID 42083731
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The electronic criterion and the recently suggested two-factor descriptor based on orbital-free density functional theory are analyzed for distinguishing different types of O-B/O···B and O-C/O···C bonding in 9-anthraceny...The electronic criterion and the recently suggested two-factor descriptor based on orbital-free density functional theory are analyzed for distinguishing different types of O-B/O···B and O-C/O···C bonding in 9-anthracenyl derivatives. These descriptors are based on the comparison of the distances of extreme positions of the electrostatic and total static potentials along the bond line. Nonclassical cases of bonding, including sterically hindered derivatives of penta-coordinated carbon and boron atoms, have also been considered using NBO analysis. It was demonstrated that both techniques provide complementary conclusions about the bonding type in the considered structures. They allow distinguishing covalent and noncovalent bonds, as well as recognizing the formation of weak O···C···O bonds.
J Phys Chem A
· 2026 May · PMID 42082205
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The energetic ordering of actinide endohedral fullerene isomers depends sensitively on proper exploration of their intramolecular potential energy surfaces. In a previous theoretical study, we predicted that the Th@C(10)...The energetic ordering of actinide endohedral fullerene isomers depends sensitively on proper exploration of their intramolecular potential energy surfaces. In a previous theoretical study, we predicted that the Th@C(10)-C isomer is the lowest-energy structure, which is in apparent contradiction with recent experiments identifying Th@C(8)-C and Th@C(15)-C as the preferentially formed isomers. Here, we theoretically reevaluate all 24 isolated-pentagon-rule Th@C isomers using systematic sampling of the thorium positions inside the carbon cage. We show that the experimentally observed isomers are indeed the lowest-energy structures when the conformational space is properly explored. The earlier misassignment is traced to convergence into higher-energy local minima caused by strong, directional Th-cage covalent interactions. Bonding analysis confirms the formal Th(IV) oxidation state, and the revised UV-vis-NIR spectra are consistent with the experimental results. Our results emphasize the importance of extensive conformational sampling for the reliable theoretical characterization of actinide endohedral fullerenes.
J Phys Chem A
· 2026 May · PMID 42081789
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Patterning graphene into nanoribbons is an efficient approach for tuning its band gap. The significant variation in band gaps among different typical types of nanoribbons highlights the importance of understanding their...Patterning graphene into nanoribbons is an efficient approach for tuning its band gap. The significant variation in band gaps among different typical types of nanoribbons highlights the importance of understanding their fundamental π-electron structures, which, however, remains systematically underexplored. Herein, acenes, building blocks of nanoribbons, are regarded as two-dimensional (2D) superatomic-molecules composed of O and F superatoms based on the 2D superatomic-molecule theory. The energy gap of acenes decreases with increasing length, resulting from the conjugation effect of P-type lone pairs (LPs) in SP-hybridized O superatom and F superatom. Several series of staggered acenes were constructed by introducing SP-hybridized O superatoms to break the overall conjugation, thereby increasing the energy gap. These staggered acenes were further extended into nanoribbons, whose band gaps are widely tuned across a broad range from 0.00 to 2.45 eV. This work reveals the role of P-type LP conjugation in governing the electronic properties of nanoribbons and provides a strategic pathway for band gap engineering in graphene-based materials.
J Phys Chem A
· 2026 May · PMID 42081319
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We have investigated the electron-transfer-mediated decay (ETMD) process associated with the Auger final state of the Ne(1s)(HO) ( = 1, 4) cluster. After core ionization of Ne, a fast Auger decay takes place, which produ...We have investigated the electron-transfer-mediated decay (ETMD) process associated with the Auger final state of the Ne(1s)(HO) ( = 1, 4) cluster. After core ionization of Ne, a fast Auger decay takes place, which produces Ne(2s), Ne(2s 2p), and Ne(2p) dications. Despite the substantially high double ionization potential for water (≈39 eV), the ETMD channel is open for Ne(2p, S) and Ne(2p, D) states. We studied the ETMD process for the S and D doubly ionized states of the Ne atom in the presence of different numbers of water molecules. Furthermore, we investigate the dependence of the ETMD decay width of the Ne(2p, S) and Ne(2p, D) states in the Ne(HO) cluster on variations in bond distance. Additionally, we examined the effect of the proton transfer process on the ETMD mechanism of the D and S doubly ionized states.
J Phys Chem A
· 2026 May · PMID 42066294
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Quantum chemical mapping of weak interaction networks in NO/HNO/HO and HNO/NO propellant systems is reported. Electrostatic potential analysis identifies HNO as the dominant hydrogen bond donor (+64.28 kcal/mol), forming...Quantum chemical mapping of weak interaction networks in NO/HNO/HO and HNO/NO propellant systems is reported. Electrostatic potential analysis identifies HNO as the dominant hydrogen bond donor (+64.28 kcal/mol), forming the strongest complex with HO (-9.45 kcal/mol). In the ternary HNO···NO···HO cluster, water acts as a polarization catalyst, inducing a cooperative stabilization of 1.99 kcal/mol by enhancing the HNO donor ability. Most significantly, in water-depleted 2HNO···NO clusters, a specific weak interaction topology prefigures a concerted double proton transfer pathway (Δ‡ = +32.1 kcal/mol), forming [HNO···NO]···NO ion pairs. This finding provides a new theoretical hypothesis for the source of ions beyond the dissociation of HNO in future studies of corrosion origin. Solvation models further confirm the persistence of these weak interaction networks and the feasibility of the proposed proton transfer pathway in the liquid NO environment.
Sheng Z, Chen X, Li K
… +6 more, Zhou J, Yu R, Li D, Li L, Yin Q, Zhu F
J Phys Chem A
· 2026 May · PMID 42065874
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The reaction mechanism between magnesium (Mg) and titanium tetrachloride (TiCl) is crucial for producing a titanium sponge. Experimental investigation is challenging due to high temperatures and chlorine's corrosiveness....The reaction mechanism between magnesium (Mg) and titanium tetrachloride (TiCl) is crucial for producing a titanium sponge. Experimental investigation is challenging due to high temperatures and chlorine's corrosiveness. The study used density functional theory combined with first-principles molecular dynamics (FPMD) at 1123 K to 1373 K to analyze the reaction mechanism. Initially, TiCl is directly reduced by Mg in a stepwise manner: TiCl → TiCl → TiCl → TiCl → Ti atoms. The intermediate TiCl species ( = 1-3) formed undergo reverse reactions and aggregate into Cl-bridged multinuclear low-valence titanium chlorides. These Cl-bridged species transform into Ti-bonded multinuclear low-valence titanium chlorides supported by MgCl. After forming Ti-bonded multinuclear species, the reduction proceeds via an electrochemically mediated reduction (EMR) pathway. In the EMR step, electrons transfer from Mg to chlorine, then from chlorine to titanium. Enhancing the electrochemical reduction step could significantly improve the overall reaction rate of Mg reducing TiCl.