Laboratoire de Physique et Chimie Théoriques

In this paper, we study finite-size effects in the Blume–Capel model through the analysis of the zeros of the partition function. We consider a complete graph and use the behavior of the partition function zeros to elucidate the crossover from effective to asymptotic properties. While in the thermodynamic limit the exact solution yields the asymptotic mean-field behavior, for finite size systems an effective critical behavior is observed. We show that even for large systems the criticality is not asymptotic. We also present insights into how partition function zeros in different complex fields (temperature, magnetic field, crystal field) give different precision and provide us with different parts of the larger picture. This includes the differences between criticality and tricriticality as seen through the lens of Fisher, Lee–Yang, and crystal field zeros.

This study offers a detailed computational analysis of the optoelectronic properties of anthraquinone (AQ) derivatives and their alkyl-substituted variants. Using density functional theory, we examine how the positioning of C 3F 3 groups affects their electronic, transport, and optical characteristics. Our findings highlight the crucial role of molecular design in tailoring these properties, with AQ crystals emerging as promising candidates for n-type organic semiconductors. We also explore the impact of adding electron-withdrawing groups, such as chlorine and bromine, which notably reduce HOMO–LUMO gaps and improve electron injection, thus enhancing device performance. These substitutions significantly alter charge transport properties, providing a straightforward strategy for designing high-performance n-type semiconductors. Overall, our work advances the understanding of AQ derivatives, offering insights that could guide the development of next-generation organic electronic devices.

Near-UV circular dichroism (CD) spectroscopy is a widely used method that provides, among others, information about the tertiary structure of biomolecular systems such as proteins, RNA, or DNA. Experimental near-UV CD spectra of proteins reflect the CD signals averaged over the many conformations that these systems can adopt. Theoretical approaches have been developed to predict such spectroscopic properties and link modeled conformations of complex biosystems to easily accessible experimental data, without having the resort to costly structural biology techniques. However, these predictions are mostly generated on the basis of a single experimental structure, missing the dynamic information reflecting the protein conformational variability. Here, we describe a complete reformulation of the theoretical foundations behind the prediction of CD spectra. We propose a QM/MM-based automated pipeline that generates an average near-UV CD spectrum from a given MD ensemble in a fast manner based on these theoretical considerations and further test it on protein systems. This pipeline has been implemented in an open-source program called DichroProt.

This study investigates the interaction between a cylindrical protein model containing a twisted hydrophobic strip and a lipid bilayer membrane with a coarse-grained simulation technique.

Considering a general microscopic model for a quantum measuring apparatus comprising a quantum probe coupled to a thermal bath, we analyze the energetic resources necessary for the realization of a quantum measurement, which includes the creation of system-apparatus correlations, the irreversible transition to a statistical mixture of definite outcomes, and the apparatus resetting. Crucially, we do not resort to another quantum measurement to capture the emergence of objective measurement results, but rather exploit the properties of the thermal bath which redundantly records the measurement result in its degrees of freedom, naturally implementing the paradigm of quantum Darwinism. In practice, this model allows us to perform a quantitative thermodynamic analysis of the measurement process. From the expression of the second law, we show how the minimal required work depends on the energy variation of the system being measured plus information-theoretic quantities characterizing the performance of the measurement – efficiency and completeness. Additionally, we show that it is possible to perform a thermodynamically reversible measurement, thus reaching the minimal work expenditure, and provide the corresponding protocol. Finally, for finite-time measurement protocols, we illustrate the increasing work cost induced by rising entropy production inherent in finite-time thermodynamic processes. This highlights an emerging trade-off between velocity of the measurement and work cost, on top of a trade-off between efficiency of the measurement and work cost. We apply those findings to bring new insights in the thermodynamic balance of the measurement-powered quantum engines.

The electron-impact ionization of water molecules at low impact energies is investigated using a theoretical approach named M3CWZ. In this model, which considers exchange effects and post-collision interaction, the continuum electrons (incident, scattered, and ejected) are all described by a Coulomb wave that corresponds to distance-dependent charges generated from the molecular target properties. Triple differential cross-sections for low impact energy ionization of either the 1b1 or 3a1 orbitals are calculated for several geometrical and kinematical configurations, all in the dipole regime. The M3CWZ model is thoroughly tested with an extensive comparison with available theoretical results and COLTRIMS measurements performed at projectile energies of Ei = 81 eV [Ren et al., Phys. Rev. A 95, 022701 (2017)] and Ei = 65 eV [Zhou et al., Phys. Rev. A 104, 012817 (2021)]. Similar to other theoretical models, an overall good agreement with both sets of measured data is observed for the angular distributions. Our calculated cross-sections’ magnitudes are also satisfactory when compared to the other theoretical results, as well as to the cross-normalized relative scale data at 81 eV impact energy. The 65 eV set of data, measured on an absolute scale, offers a further challenging task for theoretical descriptions, and globally the M3CWZ performs fairly well and comparably to other theories. The proposed approach with variable charges somehow allows to capture the main multicenter distortion effects while avoiding high computational costs.

Polyanionic alginates have a high affinity for binding divalent cations. Density functional theory studies were carried out to obtain information about COO@Metal (COO@M) interactions in metal@alginate (M@ALG) complexes after cross-linking with several cations such as Ca²⁺, Co²⁺, Cu²⁺, Ni²⁺ and Zn²⁺. The energies, interactions, and TD-DFT FTIR of metal complexes in ionotropic alginate hydrogels were investigated by DFT calculations depending on the type of metal cation. The COO@Ca, COO@Co, COO@Ni and COO@Zn interactions in their complexes all were a unidentate coordination mode is established to be the energetically most favored. The COO@Cu interaction in Cu@ALG complex was bidentate chelating coordination. Molecular electrostatic potential display that the most reactive site of the M@ALG complexes is the site containing the oxygen atom. The calculated values of free energy show the formation of a strong covalent bonding between Cu²⁺, Ni²⁺ and Zn²⁺ metal ions and carboxyl oxygen atom in alginate than the formed COO@M bonds in Ca@ALG and Co@ALG complexes. All cations used interacted significantly and strongly with the alginate. This leads to a decrease in the interaction energy of the complex. According to DFT calculations, the measured affinities are in the order Cu²⁺ > Ca²⁺ > Co²⁺ > Ni²⁺ > Zn²⁺.

Herein, we have studied the direct deoxygenation (DDO) (without prior hydrogenation) of furan, 2-methylfuran and benzofuran on the metal edge of MoS2 with a vacancy created under pressure of dihydrogen. For the three molecules, we found that the desorption of the water molecule for the regeneration of the vacancy is the most endothermic. Based on the thermodynamic and kinetic aspects, the reactivity order of the oxygenated compounds is furan ≈ 2-methylfuran > benzofuran, which is in agreement with literature. We present the key stages of the mechanisms and highlight the effects of substituents.

In cellular environments, the reduction of disulfide bonds is pivotal for protein folding and synthesis. However, the intricate enzymatic mechanisms governing this process remain poorly understood. This study addresses this gap by investigating a disulfide bridge reduction reaction, serving as a model for comprehending electron and proton transfer in biological systems. Six potential mechanisms for reducing the dimethyl disulfide (DMDS) bridge through electron and proton capture were explored. Thermodynamic and kinetic analyses elucidated the sequence of proton and electron addition. MD-PMM, a method that combines molecular dynamics simulations and quantum-chemical calculations, was employed to compute the redox potential of the mechanism. This research provides valuable insights into the mechanisms and redox potentials involved in disulfide bridge reduction within proteins, offering an understanding of phenomena that are challenging to explore experimentally. All calculations used the Gaussian 09 software package at the MP2/6–311 + g(d,p) theory level. Visualization of the molecular orbitals and electron densities was conducted using Gaussview6. Molecular dynamics simulations were performed using GROMACS with the CHARMM36 force field. The PyMM program (Python Program for QM/MM Simulations Based on the Perturbed Matrix Method) is used to apply the Perturbed Matrix Method to MD simulations.

Encapsulating Fe3C in carbon layers has emerged as an innovative strategy for protecting Fe3C while preserving its high oxygen reduction activity. However, fundamental questions persist regarding the active sites of encapsulated Fe3C due to the restricted accessibility of oxygen molecules to the metal sites. Herein, the intrinsic electron transfer mechanisms of Fe3C nanoparticles encapsulated in N‐doped carbon materials are unveiled for oxygen reduction electrocatalysis. The precision‐structured C1N1 material is used to synthesize N‐doped carbons with encapsulated Fe3C, significantly enhancing catalytic activity (EONSET = 0.98 V) and achieving near‐100% operational stability. In anion‐exchange membrane fuel cells, an excellent peak power density of 830 mW cm⁻² is reached at 60 °C. The experimental and computational results revealed that the presence of Fe3C cores dynamically triggers electron transfer to the outermost carbon layer. This phenomenon amplifies the oxygen reduction reaction performance at N sites, contributing significantly to the observed catalytic enhancement.

In this report, we show that modification of the X counterions constitutive of [Ru(bpy)3](X)2 photocatalysts modulates their catalytic activities in intermolecular [2+2] cycloaddition reactions operating through triplet-triplet energy transfer (TTEnT). Particularly noteworthy is the dramatic impact observed in low-dielectric constant solvent over the excited state quenching coefficient, which varies by two orders of magnitude depending on whether X is a large weakly bound (BArF-) or a tightly bound anion (TsO-). In addition, the counterion identity also greatly affects the photophysical properties of the cationic ruthenium complex, with [Ru(bpy)3](BArF4)2 exhibiting the shortest 3MLCT excited state lifetime, highest excited state energy and photostability, enabling remarkably enhanced performance (up to >1000 TON at low 500 ppm catalyst loading) in TTEnT photocatalysis.

This paper reports the energies and charge and spin distributions of the low-lying excited states in singlet and triplet N2V defects in diamond from direct Δ-SCF calculations based on Gaussian orbitals within the B3LYP, PBE0, and HSE06 functionals. They assign the observed absorption at 2.463 eV, first reported by Davies et al. [Proc. R. Soc. London 351, 245 (1976)], to the excitation of a N(sp³) lone-pair electron in the singlet and triplet states, respectively, with estimates of ∼1.1 eV for that of the unpaired electrons, C(sp³). In both cases, the excited states are predicted to be highly local and strongly excitonic with 81% of the C(sp³) and 87% of the N(sp³) excited charges localized at the three C atoms nearest neighbor (nn) to the excitation sites. Also reported are the higher excited gap states of both the N lone pair and C unpaired electron. Calculated excitation energies of the bonding sp³ hybrids of the C atoms nn to the four inner atoms are close to that of the bulk, which indicates that the N2V defect is largely a local defect. The present results are in broad agreement with those reported by Udvarhelyi et al. [Phys. Rev. B 96, 155211 (2017)] from plane wave HSE06 calculations, notably for the N lone pair excitation energy, for which both predict an energy of ∼2.7 eV but with a difference of ∼0.5 eV for the excitation of the unpaired electron.

Understanding the mechanistic of carbon dioxide (CO2) hydrogenation reaction (HR) to methanol is a major goal, as it is an attractive approach to mitigate CO2 emissions by converting them into...