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Why are DNA bases stacked in a double helix structure? We combined three theoretical approaches to demonstrate how one core concept derived from quantum mechanics (Pauli repulsion) annihilates the contribution of dispersion to the π-π stacking. The helical architecture is governed by a combination of exchange and electrostatic forces, a result that is interpreted from both a computational and a biological perspective.
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The emergence of correlated phenomena arising from the combination of 1T and 1H van der Waals layers is the focus of intense research. Here, we synthesize a self-stacked 6R phase in NbSeTe, showing perfect alternating 1T and 1H layers that grow coherently along the c-direction, as revealed by scanning transmission electron microscopy. Angle-resolved photoemission spectroscopy shows a mixed contribution of the trigonal and octahedral Nb bands to the Fermi level. Diffuse scattering reveals temperature-independent short-range charge fluctuations with propagation vector qCO = (0.25 0), derived from the condensation of a longitudinal mode in the 1T layer, while the long-range charge density wave is quenched by ligand disorder. Magnetization measurements suggest the presence of an inhomogeneous, short-range magnetic order, further supported by the absence of a clear phase transition in the specific heat. These experimental analyses in combination with ab initio calculations indicate that the ground state of 6R-NbSeTe is described by a statistical distribution of short-range charge-modulated and spin-correlated regions driven by ligand disorder. Our results demonstrate how natural 1T-1H self-stacked bulk heterostructures can be used to engineer emergent phases of matter.
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Theoretical design of molecular superbases has been attracting researchers for more than twenty years. General approaches were developed to make the bases potentially stronger, but less attention was paid to the stability of the predicted structures. Hence, only a small fraction of the theoretical research has led to positive experimental results. Possible stability issues of extremely strong bases are extensively studied in this work using quantum chemical calculations on a high level of theory. Several step-by-step design examples are discussed in detail, and general recommendations are given to avoid the most common stability problems. New potentially stable structures are theoretically studied to demonstrate the future prospects of molecular superbases design.
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The efficiency of catalysts relies on comprehending the underlying kinetics that govern their performance. Under the steady-state regime, the "rate" is referred to as the turnover frequency, where the reaction rate is first order with respect to catalysts. Here, we introduce the Maximum Kinetic Efficiency (MaxKinEff ) model, grounded in collision theory, to predict efficiency based on maximum turnover frequency, ð¤max TOF0 and maximum turnover number, ðmax TON0. The model was applied to molecular water oxidation using twenty-six transition metal catalysts from the first (3d), second (4d), and third (5d) rows. A thorough investigation reveals that [Ru(pda)(Br-py)2] (pda = 1,10-phenanthroline-2,9-dicarboxylate; Py = pyridinophane) exhibits a notable ð¤max TOF0 of 1176.87 × 10-5 s-1 due to its larger collision diameter (σð ð¶) and lower activation energy (Eð). Importantly, the trend in the computed ðmax TON0 values aligns with experimental TON, ðexperimental TON validating the model's accuracy. For instance, [Cp∗Ir(κ2-N,O)NO3] is identified by MaxKinEff as a standout performer, with the normalized maximum computed TON, ðmax TON0 resembling the experimental TON, ðexperimental TON = 2000.
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New cobalt(II)-based complexes with [N2O2] coordination formed by two bis-chelate ligands were synthesized and characterized by a multi-technique approach. The complexes possess an easy-axis anisotropy (D < 0) and magnetic measurements show a field-induced slow relaxation of magnetization. The spin-reversal barriers, i.e., the splitting of the two lowest Kramers doublets (UZFS), have been measured by THz-EPR spectroscopy, which allows to distinguish the two crystallographically independent species present in one of the complexes. Based on these experimental UZFS energies together with those for related complexes reported in literature, it was possible to establish magneto-structural correlations. UZFS linearly depends on the elongation parameter εT of the (pseudo-)tetrahedral coordination, which is given by the ratio between the average obtuse and acute angles at the cobalt(II) ion, while UZFS was found to be virtually independent of the twist angle of the chelate planes. With increasing deviation from the orthogonality of the latter, the rhombicity (|E/D|) increases.
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Quantum information theory provides a powerful toolbox of descriptors that characterize many-electron systems based on quantum information patterns between open quantum systems. Despite the wealth of insights gained in the con- densed matter community, the use of these descriptors to study interactions between atoms in a molecule remains limited. In this study, we develop a quantum information framework for molecules that characterizes the quantum in- formation patterns between quantum atoms as defined in the Quantum Theory of Atoms in Molecules. We show that quantum information analyses capture key properties of quantum atoms and how they interact with their molec- ular environment. Additionally, we show that the presence of bond critical points can remain invariant despite large changes in the quantum information patterns between the quantum atoms. Our findings indicate that quantum infor- mation theory can shed a new light on molecular electronic structure.
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This article introduces a suite of mini-applications (mini-apps) designed to optimise computational kernels in ab initio electronic structure codes. The suite is developed from flagship applications participating in the NOMAD Center of Excellence, such as the ELPA eigensolver library and the GW implementations of the exciting, Abinit, and FHI-aims codes. The mini-apps were identified by targeting functions that significantly contribute to the total execution time in the parent applications. This strategic selection allows for concentrated optimisation efforts. The suite is designed for easy deployment on various High-Performance Computing (HPC) systems, supported by an integrated CMake build system for straightforward compilation and execution. The aim is to harness the capabilities of emerging (post)exascale systems, which necessitate concurrent hardware and software development - a concept known as co-design. The mini-app suite serves as a tool for profiling and benchmarking, providing insights that can guide both software optimisation and hardware design. Ultimately, these developments will enable more accurate and efficient simulations of novel materials, leveraging the full potential of exascale computing in material science research.
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This article reports the synthesis, along with structural and photophysical characterization of 2-(2'-hydroxyphenyl)benzazole derivatives functionalized with various azaheterocycles (pyridine, pyrimidine, terpyridine). These compounds show dual-state emission properties, that is intense fluorescence both in solution and in the solid-state with a range of fluorescent color going from blue to orange. Moreover, the nature of their excited state can be tuned by the presence of external stimuli such as protons or metal cations. In the absence of stimuli, these dyes show emission stemming from anionic species obtained after deprotonation (D* transition), whereas upon protonation or metal chelation, ESIPT process occurs leading to a stabilized and highly emissive K* transition. With the help of extensive ab initio calculations, we confirm that external stimuli can switch the nature of the transitions, making this series of dyes attractive candidates for the development of stimuli-responsive fluorescent ratiometric probes.
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Transition metal dichalcogenide TiSe2 exhibits a superconducting dome within a low pressure range of 2-4 GPa, which peaks with the maximal transition temperature Tc of ≈1.8 K. Here it is reported that applying high pressure induces a new superconducting state in TiSe2, which starts at ≈16 GPa with a substantially higher Tc that reaches 5.6 K at ≈21.5 GPa with no sign of decline. Combining high-throughput first-principles structure search, X-ray diffraction, and Raman spectroscopy measurements up to 30 GPa, It is found that TiSe2 undergoes a first-order structural transition from the 1T phase under ambient pressure to a new 4O phase under high pressure. Comparative ab initio calculations reveal that while the conventional phonon-mediated pairing mechanism may account for the superconductivity observed in 1T-TiSe2 under low pressure, the electron-phonon coupling of 4O-TiSe2 is too weak to induce a superconducting state whose transition temperature is as high as 5.6 K under high pressure. The new superconducting state found in pressurized TiSe2 requires further study on its underlying mechanism.
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Against the general belief that carbonic acid is too unstable for synthesis, it was possible to synthesize the solid as well as gas-phase carbonic acid. It was suggested that solid carbonic acid might exist in Earth's upper troposphere and in the harsh environments of other solar bodies, where it undergoes a cycle of synthesis, decomposition, and dimerization. To provide spectroscopic data for probing the existence of extraterrestrial carbonic acid, matrix-isolation infrared (MI-IR) spectroscopy has shown to be essential. However, early assignments within the harmonic approximation using scaling factors impeded a full interpretation of the rather complex MI-IR spectrum of H2CO3. Recently, carbonic acid was detected in the Galactic center molecular cloud and triggered new interest in the anharmonic spectrum. In this regard, we substantially reassign our Argon MI-IR spectra relying on accurate anharmonic calculations. We calculate a four-mode potential energy surface (PES) at the explicitly correlated coupled-cluster theory using up to triple-zeta basis sets, i.e., CCSD(T)-F12/cc-pVTZ-F12. On this PES, we perform vibrational self-consistent field and configuration interaction (VSCF/VCI) calculations to obtain accurate vibrational transition frequencies and resonance analysis of the fundamentals, first overtones, and combination bands.
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The rich phenomenology of quantum many-body systems such as atomic nuclei is complex to interpret. Often, the behaviour (e.g. evolution with the number of constituents) of measurable/observable quantities such as binding or excitation energies can be best understood based on a simplified picture involving auxiliary quantities that are not observable, i.e. whose values vary with parameters that are internal to the theoretical construction (contrarily to measurable/observable quantities). While being useful, the simplified interpretation is thus theoretical-scheme dependent. This applies, in particular, to the so-called single-nucleon shell structure based on auxiliary effective single-particle energies (ESPEs). In this context, the present work aims at (i) recalling the way to compute ESPEs out of solutions of many-body Schrödinger's equation, (ii) illustrating the use of ESPEs within the frame of state-of-the-art ab initio calculations to interpret the outcome of a recent nuclear experiment, and (iii) demonstrating the impact of several alterations on the computation of ESPEs. While the chosen alterations constitute approximations within the ab initio scheme, they are built-in when employing other theoretical constructs at play in nuclear physics. The present considerations are thus meant to empirically illustrate variations that can be expected between ESPEs computed within different (equally valid) theoretical schemes. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'.
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Herein, a self-supported, robust, and noble-metal-free 3D hierarchical interface-rich Fe-doped Co-LDH@MoS2-Ni3S2/NF heterostructure electrocatalyst has been prepared through a controllable two-step hydrothermal process. The resultant electrode shows low overpotential of ~95â mV for hydrogen evolution reaction (HER), ~220â mV for the oxygen evolution reaction (OER), and the two-electrode system requires only a cell voltage of ~1.54â V at 10â mA cm-2 current density, respectively. Extensive ab initio calculations were carried out to find out the overpotential for HER, orbital interaction through the determination of electron density of states and quantification of charge transfer by Bader charge analysis. The computed overpotential matched closely with the experimental data. The superior HER performance of the tri-layer is enhanced due to the charge transfer (1.7444â e) to Fe-doped Co-LDH from Ni3S2-MoS2 hybrid. This research strategy paves an effective pathway for affordable green H2 production and future efficient non-precious bifunctional electrocatalyst design for overall water electrolysis.
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The discovery of covalent H3S and clathrate structure LaH10 with excellent superconducting critical temperatures at high pressures has facilitated a multitude of research on compressed hydrides. However, their superconducting pressures are too high (generally above 150 GPa), thereby hindering their application. In addition, making room-temperature superconductivity close to ambient pressure in hydrogen-based superconductors is challenging. In this work, we calculated the chemically "pre-compressed" Be-H by heavy metals Th and Ce to stabilize the superconducting phase near ambient pressure. An unprecedented ThBeH8 (CeBeH8) with a "fluorite-type" structure was predicted to be thermodynamically stable above 69 GPa (76 GPa), yielding a T c of 113 K (28 K) decompressed to 7 GPa (13 GPa) by solving the anisotropic Migdal-Eliashberg equations. Be-H vibrations play a vital role in electron-phonon coupling and structural stability of these ternary hydrides. Our results will guide further experiments toward synthesizing ternary hydride superconductors at mild pressures.
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A new Co(II) complex, [Co(NCS)2(L)2] (1) has been synthesized based on levamisole (L) as a new ligand. Single-crystal X-ray diffraction analyses confirm that the Co(II) ion is having a distorted tetrahedral coordination geometry in the complex. Notably strong intramolecular Sâ â â S and Sâ â â N interactions has been confirmed by employing Quantum Theory of Atoms in Molecules (QTAIM). These intramolecular interactions occur among the sulfur and nitrogen atoms of the levamisole ligands and also the nitrogen atoms of the thiocyanate. Direct current (dc) magnetic analyses reveal presence of zero field splitting (ZFS) and large magnetic anisotropy on Co(II). Detailed ab initio ligand field theory calculations quantitatively predicted the magnitude of ZFS. Prominent field-induced single-ion magnet (SIM) behavior was observed for 1 from dynamic magnetization measurements. Slow magnetic relaxation follows an Orbach mechanism with the effective energy barrier Ueff=29.6 (7)â K and relaxation time τo=1.4 (4)×10-9â s.
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The microwave spectrum of 1-cyanopropene (crotonitrile) was remeasured using two pulsed molecular jet Fourier transform microwave spectrometers operating from 2.0 to 40.0 GHz. The molecule exists in two isomer forms, E and Z, with respect to the orientation between the methyl and the cyano groups. The spectrum of the Z isomer is more intense. Due to internal rotation of the methyl group, doublets containing A and E torsional species were found for all rotational transitions. Hyperfine splittings arising from the 14N nuclear quadrupole coupling were resolved. The heavy atom structure of the Z isomer was determined by observation of 13C and 15N isotopologue spectra in natural abundances. The experimental results were supported by quantum chemistry. The complex spectral patterns were analyzed and fitted globally, and the barriers to methyl internal rotation are determined to be 478.325(28) cm-1 and 674.632(76) cm-1 for the Z and E isomers, respectively. The non-bonded intramolecular electrostatic attraction between the methyl group and the 1-cyano substituent overcomes steric hindrance, leading to higher stability of the Z isomer. The consequence is a slight opening of 3.2° of the C(1)-C(2)-C(3) angle and a radical decrease of the methyl torsional barrier in the Z isomer due to steric repulsion.
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Supercritical water provides distinctly different solvation properties compared to what is known from liquid water. Despite its prevalence deep in the Earth's crust and its role in chemosynthetic ecosystems in the vicinity of hydrothermal vents, molecular insights into its solvation mechanisms are still very scarce compared to what is known for liquid water. Recently, neutral metal particles have been detected in hydrothermal fluids and proposed to explain the transport of gold species to ore deposits on Earth. Using ab initio molecular dynamics, we elucidate the solvation properties of small gold species at supercritical conditions. The neutral metal clusters themselves contribute enormous THz intensity not because of their intramolecular vibrations, but due to their pronounced electronic polarization coupling to the dynamical supercritical solvent, leading to a continuum absorption up to about 1000â cm-1. On top, long-lived interactions between the gold clusters and solvation water leads at these supercritical conditions to a sharp THz resonance that happens to be close to the one due to H-bonding in liquid water at ambient conditions. The resulting distinct resonances can be used to analyse the solvation properties of neutral metal particles in supercritical aqueous solutions.
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2,5-bis(hydroxymethyl)furan (BHMF) derived from 5-Hydroxymethylfurfural (HMF) through a hydrogenation process has extensive applications in the production of resins, polymers, and artificial fibers. However, screening out the candidate and then modulating the active site to optimize the catalyst for high yield of BHMF are currently insufficient. In this study, Gibbs free energy diagrams of the reduction of HMF on 13 metals were presented, along with the identification of the rate-determining step (RDS) with the highest reaction barrier for each metal. We attempted to construct a volcano plot for HMFRR reaction. Additionally, a strategy was proposed to adjust the reaction barriers of RDS by combining two appropriate metals. Further experiments confirmed that Pb with the lowest energy barrier exhibited the highest HMF conversion (BHMF selectivity) among single metals. The modified catalyst by doping Ag on Pb, further boosted the HMF conversion (BHMF selectivity) from 42.1 % (59.4 %) to 80.8 % (80.9 %), respectively. These results provide an approach to rationally design and construct the catalyst system for efficient conversion of HMF.
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Quantum computers are expected to outperform classical computers for specific problems in quantum chemistry. Such calculations remain expensive, but costs can be lowered through the partition of the molecular system. In the present study, partition was achieved with range-separated density functional theory (RS-DFT). The use of RS-DFT reduces both the basis set size and the active space size dependence of the ground state energy in comparison with the use of wave function theory (WFT) alone. The utilization of pair natural orbitals (PNOs) in place of canonical molecular orbitals (MOs) results in more compact qubit Hamiltonians. To test this strategy, a basis-set independent framework, known as multiresolution analysis (MRA), was employed to generate PNOs. Tests were conducted with the variational quantum eigensolver for a number of molecules. The results show that the proposed approach reduces the number of qubits needed to reach a target energy accuracy.
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In the last two decades, significant efforts have been particularly invested in two-dimensional (2D) hexagonal boron carbon nitride h-BxCyNz because of its unique physical and chemical characteristics. The presence of the carbon atoms lowers the large gap of its cousin structure, boron nitride (BN), making it more suitable for various applications. Here, we use density functional theory to study the structural, electronic, and magnetic properties of Pt-doped BC6N (Pt-BC6N, as well as its adsorption potential of small molecular gases (NO, NO2, CO2, NH3). We consider all distinct locations of the Pt atom in the supercell (B, N, and two C sites). Different adsorption locations are also considered for the pristine and Pt-doped systems. The formation energies of all Pt-doped structures are close to those of the pristine system, reflecting their stability. The pristine BC6N is semiconducting, so doping with Pt at the B and N sites gives a diluted magnetic semiconductor while doping at the C1 and C2 sites results in a smaller gap semiconductor. We find that all doped structures exhibit direct band gaps. The studied molecules are very weakly physisorbed on the pristine structure. Pt doping leads to much stronger interactions, where NO, NO2, and NH3 chemisorb on the doped systems, and CO2 physiorb, illustrating the doped systems' potential for gas purification applications. We also find that the adsorption changes the electronic and magnetic properties of the doped systems, inviting their consideration for spintronics and gas sensing.