index - Méthodes et outils de la chimie quantique Access content directly

Last deposit, any kind of documents

Abstract Chiral molecules, used in applications such as enantioselective photocatalysis 1 , circularly polarized light detection 2 and emission 3 and molecular switches 4,5 , exist in two geometrical configurations that are non-superimposable mirror images of each other. These so-called ( R ) and ( S ) enantiomers exhibit different physical and chemical properties when interacting with other chiral entities. Attosecond technology might enable influence over such interactions, given that it can probe and even direct electron motion within molecules on the intrinsic electronic timescale 6 and thereby control reactivity 7–9 . Electron currents in photoexcited chiral molecules have indeed been predicted to enable enantiosensitive molecular orientation 10 , but electron-driven chiral dynamics in neutral molecules have not yet been demonstrated owing to the lack of ultrashort, non-ionizing and perturbative light pulses. Here we use time-resolved photoelectron circular dichroism (TR-PECD) 11–15 with an unprecedented temporal resolution of 2.9 fs to map the coherent electronic motion initiated by ultraviolet (UV) excitation of neutral chiral molecules. We find that electronic beatings between Rydberg states lead to periodic modulations of the chiroptical response on the few-femtosecond timescale, showing a sign inversion in less than 10 fs. Calculations validate this and also confirm that the combination of the photoinduced chiral current with a circularly polarized probe pulse realizes an enantioselective filter of molecular orientations following photoionization. We anticipate that our approach will enable further investigations of ultrafast electron dynamics in chiral systems and reveal a route towards enantiosensitive charge-directed reactivity.

Continuer la lecture Partager

In this work an approximate analytic expression for the quantum partition function of the quartic oscillator described by the potential $V(x) = \frac{1}{2} \omega^2 x^2 + g x^4$ is presented. Using a path integral formalism, the exact partition function is approximated by the partition function of a harmonic oscillator with an effective frequency depending both on the temperature and coupling constant $g$. By invoking a Principle of Minimal Sensitivity (PMS) of the path integral to the effective frequency, we derive a mathematically well-defined analytic formula for the partition function. Quite remarkably, the formula reproduces qualitatively and quantitatively the key features of the exact partition function. The free energy is accurate to a few percent over the entire range of temperatures and coupling strengths $g$. Both the harmonic ($g\rightarrow 0$) and classical (high-temperature) limits are exactly recovered. The divergence of the power series of the ground-state energy at weak coupling, characterized by a factorial growth of the perturbational energies, is reproduced as well as the functional form of the strong-coupling expansion along with accurate coefficients. Explicit accurate expressions for the ground- and first-excited state energies, $E_0(g)$ and $E_1(g)$ are also presented.

Continuer la lecture Partager

Short-range corrections to long-range selected configuration interaction calculations are derived from perturbation theory considerations and applied to harmonium (with two to six electrons for some low-lying states). No fitting to reference data is used, and the method is applicable to ground and excited states. The formulas derived are rigorous when the physical interaction is approached. In this regime, the second-order expression provides a lower bound to the long-range full configuration interaction energy. A long-range/short-range separation of the interaction between electrons at a distance of the order of one atomic unit provides total energies within chemical accuracy, and, for the systems studied, provide better results than short-range density functional approximations.

Continuer la lecture Partager

Electronic resonances are metastable states that can decay by electron loss. They are ubiquitous across various fields of science, such as chemistry, physics, and biology. However, current theoretical and computational models for resonances cannot yet rival the level of accuracy achieved by bound-state methodologies. Here, we generalize selected configuration interaction (SCI) to treat resonances using the complex absorbing potential (CAP) technique. By modifying the selection procedure and the extrapolation protocol of standard SCI, the resulting CAP-SCI method yields resonance positions and widths of full configuration interaction quality. Initial results for the shape resonances of \ce{N2-} and \ce{CO-} reveal the important effect of high-order correlation, which shifts the values obtained with CAP-augmented equation-of-motion coupled-cluster with singles and doubles by more than \SI{0.1}{\eV}. The present CAP-SCI approach represents a cornerstone in the development of highly-accurate methodologies for resonances.

Continuer la lecture Partager

ipie is a Python-based auxiliary-field quantum Monte Carlo (AFQMC) package that has undergone substantial improvements since its initial release [J. Chem. Theory Comput., 2022, 19(1): 109-121]. This paper outlines the improved modularity and new capabilities implemented in ipie. We highlight the ease of incorporating different trial and walker types and the seamless integration of ipie with external libraries. We enable distributed Hamiltonian simulations, allowing for multi-GPU simulations of large systems. This development enabled us to compute the interaction energy of a benzene dimer with 84 electrons and 1512 orbitals, which otherwise would not have fit on a single GPU. We also support GPU-accelerated multi-slater determinant trial wavefunctions [arXiv:2406.08314] to enable efficient and highly accurate simulations of large-scale systems. This allows for near-exact ground state energies of multi-reference clusters, [Cu$_2$O$_2$]$^{2+}$ and [Fe$_2$S$_2$(SCH$_3$)]$^{2-}$. We also describe implementations of free projection AFQMC, finite temperature AFQMC, AFQMC for electron-phonon systems, and automatic differentiation in AFQMC for calculating physical properties. These advancements position ipie as a leading platform for AFQMC research in quantum chemistry, facilitating more complex and ambitious computational method development and their applications.

Continuer la lecture Partager

Subjets

Atomic data Atomic charges Ion Pesticide 3115am Rydberg states Fonction de Green Atom 3315Fm Dirac equation Quantum Monte Carlo 3115vj Electron correlation Diatomic molecules Parity violation X-ray spectroscopy Xenon Density functional theory Spin-orbit interactions Parallel speedup Polarizabilities Anderson mechanism AB-INITIO CALCULATION Approximation GW Time reversal violation Petascale Line formation Argile Auto-énergie Time-dependent density-functional theory Single-core optimization 3470+e Biodegradation Atomic and molecular collisions Large systems Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares Atomic processes Relativistic quantum mechanics Molecular properties Relativistic corrections Electron electric moment Configuration interaction Chemical concepts Acrolein Quantum Chemistry Perturbation theory Ab initio calculation Atoms 3115aj Atrazine BENZENE MOLECULE A priori Localization Numerical calculations CIPSI New physics Adiabatic connection Wave functions Electron electric dipole moment Range separation Configuration Interaction Corrélation électronique Atomic and molecular structure and dynamics Théorie des perturbations Aimantation Coupled cluster 3115bw Diffusion Monte Carlo Quantum chemistry BIOMOLECULAR HOMOCHIRALITY BSM physics Green's function Dipole 3115ae CP violation Atomic charges chemical concepts maximum probability domain population Ground states Chimie quantique États excités 3115ag AB-INITIO ALGORITHM Dispersion coefficients Abiotic degradation Carbon Nanotubes A posteriori Localization 3115vn Molecular descriptors Excited states Hyperfine structure Valence bond Analytic gradient Coupled cluster calculations Mécanique quantique relativiste AROMATIC-MOLECULES QSAR Configuration interactions Argon Relativistic quantum chemistry Azide Anion Atrazine-cations complexes

Statistics

Number of files submitted

240

Number of notices submitted

278