P2-type NaxMO2 layered oxides (x < 1) are highly promising cathodes for Na-ion batteries (NIBs) but suffer from phase transitions, transition-metal (TM) migration, and structural distortions that limit cycling stability. Here, we combine first-principles modeling and electrochemical measurements to elucidate how configurational entropy governs their structural and electronic response. By comparing low-, medium-, and high-entropy compositions, we show that higher configurational entropy mitigates TM-centered octahedral distortions, suppresses shear-type deformations associated with P2 -> O2 transitions via layer gliding, and distributes redox activity across multiple cations (Ni, Co, Fe), avoiding local over-oxidation. Defect-formation analyses reveal that high-entropy mixing significantly discourages out-of-layer TM migration, reducing TM/Na-vac antisite formation and stabilizing the layered framework upon deep desodiation. Consistently, medium- and high-entropy materials exhibit superior capacity retention and structural reversibility compared to the low-entropy analogue, with further performance enhancement when using room-temperature ionic-liquid (RTIL)-based NaFSI-Pyr(14)FSI electrolyte, which mitigates Mn dissolution and accounts for enhanced efficiency upon cycling. These findings demonstrate that configurational entropy is a powerful design parameter for achieving robust, high-performance P2-type layered cathodes and provide clear guidelines for entropy-assisted materials engineering in next-generation NIBs.
The number of accurate equilibrium structures of organic radicals is still limited, despite the central role of these species in atmospheric and combustion chemistry, spectroscopy, and catalysis. Because equilibrium structures are experimentally inaccessible for all but the smallest radicals, reliable and predictive quantum-chemical protocols are essential. While double-hybrid density functionals can achieve remarkable accuracy for closed-shell molecules, their performance often deteriorates for delocalized open-shell systems, and they may require spin- and multiplicity-dependent bond-length corrections that compromise the smoothness of potential energy surfaces. Here, we show that a local correlation treatment based on pair natural orbitals (PNOs) provides a robust and practical solution to this long-standing problem. In particular, the PNO-LCCSD(F12b)(T*) approach, embedded in an efficient composite framework, enables near-spectroscopic equilibrium geometries for both closed- and open-shell molecular systems containing up to a few dozen atoms. To make this strategy broadly accessible, we extend a previously introduced external utility to PNO-based correlated methods, enabling the automated assembly of composite gradients. Starting from DFT geometries and Hessians, local correlation is combined with hierarchical optimization and an efficient driver in generalized internal coordinates, yielding the PPCS2 protocol. Benchmark tests on a diverse set of σ-, π-, aromatic, and heteroatom-centered radicals demonstrate uniform accuracy across the full data set and deliver high-precision equilibrium structures even for reactive radicals that remain challenging to characterize experimentally.
Vibrational spectra convey a wealth of structural and dynamical information; however, their reliable assignment and interpretation often benefit from the integration of complementary spectroscopic techniques and require the support of accurate quantum chemical calculations. The harmonic approximation is frequently insufficient for quantitative spectroscopy, while fully anharmonic treatments rapidly become computationally prohibitive for large and flexible molecular systems, in particular, for biomolecules. In this framework, we introduce a general perturb-then-diagonalize approach that relies on a three-class partitioning of normal modes into primary, auxiliary, and spectator subsets and combines numerical strategies based on analytical Hessians and analytical gradients. Accurate anharmonic contributions are explicitly included for the modes of primary interest, while the influence of external modes is accounted for through finite differences of analytical gradients, avoiding the much more expensive evaluation of Hessians. Several case studies demonstrate the robustness, ease of use, and accuracy of the proposed approach across a broad range of molecular systems, including situations in which vibrational and rotational spectroscopic data provide complementary information. When combined with a dual-level strategy in which accurate methods are employed for harmonic terms and less expensive methods for anharmonic contributions, the present framework enables vibrational spectra of near-spectroscopic accuracy for biomolecules and other chemically rich systems. More complex environments can be addressed by coupling the method with multilayer approaches.
An affordable and scalable computational strategy rooted in the Pisa Composite Schemes (PCS) framework is applied to the challenging case of substituted aromatic nitriles, delivering accurate molecular structures together with rotational and vibrational spectroscopic parameters at a computational cost comparable to that of standard density functional theory. Two semiexperimental (SE) equilibrium structures are derived from high-resolution rotational spectroscopy combined with computed vibrational corrections. These structures are found to be significantly more accurate than literature substitution (rs) geometries, thus providing stringent reference data for method validation. For one system, the fully parameter-free PPCS2 approach also offers an independent and consistent structural cross-check. Building on these benchmarks, a cost-effective dual-level strategy combining double-hybrid equilibrium geometries and harmonic force fields with hybrid-level anharmonic contributions is identified as an efficient operative level of theory (DPCS3//HPCS2). Further refinement of selected bond lengths through one-parameter effective corrections (BDPCS3 model) yields ground-state rotational constants in excellent agreement with the experiment, with typical deviations well below 0.1%. The validated protocol is applied to ethynylbenzonitrile (EBN) and hydroxybenzonitrile (HBN) isomers, yielding anharmonic infrared spectra in outstanding agreement with the experiment for the ortho and para HBN species and providing predictive, high-confidence reference data for the remaining isomers. Overall, this work demonstrates that near-spectroscopic accuracy for both rotational and vibrational observables can be achieved at affordable computational cost by treating electronic correlation and vibrational effects on an equal footing, thereby enabling reliable multispectroscopic characterization of substituted aromatic nitriles of astrochemical relevance.
Current research efforts are focused on replacing chemical compounds with high-value natural products. Accordingly, fucoidans which are a predominant bioactive compounds in seaweeds, showed promising biological and pharmacological potential. In this study, we aimed to extract, characterize and evaluate the antioxidant, anti-inflammatory and antinociceptive activities of fucoidan (Fuc-Sarg) from the brown seaweed Sargassum vulgare C. Agarth collected from Salammbo coast, Tunisia. Fuc-Sarg was isolated and characterized by different techniques as colorimetric and turbidimetric assays, Fourier-Transform Infrared spectroscopy (FTIR), 1H NMR spectroscopy, Size-Exclusion Chromatography (SEC) and Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Results showed that Fuc-Sarg was obtained with an extraction yield of 3.34%, including 67.75% of total sugars, 21.10% of uronic acids, 13.5% sulfate groups and a low protein content (0.6%). FTIR and NMR analysis confirmed the presence of sulfated fucopyranose residues, while SEC showed a high molecular weight (Mw = 500,000 g/mol) with a dispersity of 13.8. Besides, GC-MS analysis revealed a heterogeneous monosaccharides composition including (arabinose, xylose, galactose, and L-fucose). However, the evaluation of the antioxidant potential of the fucoidan fraction was carried out using FRAP and DPPH assays. Results demonstrated a strong reducing power and free radical scavenging activity (IC50 = 21.2 mu g/mL). Pharmacological evaluation, in vivo, demonstrated significant dose-dependent anti-inflammatory effects in the xylene-induced ear edema model (up to 84.97% inhibition percentage) and interesting antinociceptive potential in hot plate and abdominal constriction writhing tests. These findings highlight the pharmacological therapeutic potential of fucoidan extracted from S. vulgare as a promising natural agent.
