Julien Pilmé

Introducing the ELF Topological Analysis in the Field of Quasirelativistic Quantum Calculations.

We present an original formulation of the electron localization function (ELF) in the field of relativistic two-component DFT calculations. Using I2 and At2 species as a test set, we show that the ELF analysis is suitable to evaluate the spin-orbit effects on the electronic structure. Beyond these examples, this approach opens up new opportunities for the bonding analysis of large molecular systems involving heavy and superheavy elements.

New insights in quantum chemical topology studies using numerical grid‐based analyses

New insights in Quantum Chemical Topology of one‐electron density functions have been proposed here by using a recent grid‐based algorithm (Tang et al., J Phys Condens Matter 2009, 21, 084204), initially designed for the decomposition of the electron density. Beyond the charge analysis, we show that this algorithm is suitable for different scalar functions showing a more complex topology, that is, the Laplacian of the electron density, the electron localization function (ELF), and the molecular electrostatic potential (MEP). This algorithm makes use of a robust methodology enabling to numerically assign the data points of three‐dimensional grids to basin volumes, and it has the advantage of requiring only the values of the scalar function without details on the wave function used to build the grid. Our implementation is briefly outlined (program named TopChem), its capabilities are examined, and technical aspects in terms of CPU requirement and accuracy of the results are discussed. Illustrative examples for individual molecules and crystalline solids obtained with gaussian and plane‐wave‐based density functional theory calculations are presented. Special attention was given to the MEP because its topological analysis is complex and scarce.

QTAIM Analysis in the Context of Quasirelativistic Quantum Calculations

Computational chemistry currently lacks ad hoc tools for probing the nature of chemical bonds in heavy and superheavy-atom systems where the consideration of spin-orbit coupling (SOC) effects is mandatory. We report an implementation of the Quantum Theory of Atoms-In-Molecules in the framework of two-component relativistic calculations. Used in conjunction with the topological analysis of the Electron Localization Function, we show for astatine (At) species that SOC significantly lowers At electronegativity and boosts its propensity to make charge-shift bonds. Relativistic spin-dependent effects are furthermore able to change some bonds from mainly covalent to charge-shift type. The implication of the disclosed features regarding the rationalization of the labeling protocols used in nuclear medicine for (211)At radioisotope nicely illustrates the potential of the introduced methodology for investigating the chemistry of (super)heavy elements.

Topological analyses of time-dependent electronic structures: application to electron-transfers in methionine enkephalin

We have studied electron transfers (ET) between electron donors and acceptors, taking as illustrative example the case of ET in methionine enkephalin. Recent pulse and gamma radiolysis experiments suggested that an ultrafast ET takes place from the C-terminal tyrosine residue to the N-terminal, oxidized, methionine residue. According to standard theoretical frameworks like the Marcus theory, ET can be decomposed into two successive steps: i) the achievement through thermal fluctuations, of a set of nuclear coordinates associated with degeneracy of the two electronic states, ii) the electron tunneling from the donor molecular orbital to the acceptor molecular orbital. Here, we focus on the analysis of the time-dependent electronic dynamics during the tunneling event. This is done by extending the approaches based on the topological analyses of stationary electronic density and of the electron localization function (ELF) to the time-dependent domain. Furthermore, we analyzed isosurfaces of the divergence of the current density, showing the paths that are followed by the tunneling electron from the donor to the acceptor. We show how these functions can be calculated with constrained density functional theory. Beyond this work, the topological tools used here can open up new opportunities for the electronic description in the time-dependent domain.

Electronic structures and geometries of the XF3 (X = Cl, Br, I, At) fluorides

The potential energy surfaces of the group 17 XF3 (X = Cl, Br, I, At) fluorides have been investigated for the first time with multiconfigurational wave function theory approaches. In agreement with experiment, bent T-shaped C(2v) structures are computed for ClF3, BrF3, and IF3, while we predict that an average D(3h) structure would be experimentally observed for AtF3. Electron correlation and scalar relativistic effects strongly reduce the energy difference between the D(3h) geometry and the C(2v) one, along the XF3 series, and in the X = At case, spin-orbit coupling also slightly reduces this energy difference. AtF3 is a borderline system where the D(3h) structure becomes a minimum, i.e., the pseudo-Jahn-Teller effect is inhibited since electron correlation and scalar-relativistic effects create small energy barriers leading to the global C(2v) minima, although both types of effects interfere.

211 At-labeled agents for alpha-immunotherapy: On the in vivo stability of astatine-agent bonds

The application of (211)At to targeted cancer therapy is currently hindered by the rapid deastatination that occurs inxa0vivo. As the deastatination mechanism is unknown, we tackled this issue from the viewpoint of the intrinsic properties of At-involving chemical bonds. An apparent correlation has been evidenced between inxa0vivo stability of (211)At-labeled compounds and the At-R (Rxa0=xa0C, B) bond enthalpies obtained from relativistic quantum mechanical calculations. Furthermore, we highlight important differences in the nature of the At-C and At-B bonds of interest, e.g. the opposite signs of the effective astatine charges, which implies different stabilities with respect to the biological medium. Beyond their practical use for rationalizing the labeling protocols used for (211)At, the proposed computational approach can readily be used to investigate bioactive molecules labeled with other heavy radionuclides.

Electron localization function from density components

This work addresses the decomposition of the Electron Localization Function (ELF) into partial density contributions using an appealing split of kinetic energy densities. Regarding the degree of the electron localization, the relationship between ELF and its usual spin‐polarized formula is discussed. A new polarized ELF formula, built from any subsystems of the density, and a localization function, quantifying the measure of electron localization for only a subpart of the total system are introduced. The methodology appears tailored to describe the electron localization in bonding patterns of subsystems, such as the local nucleophilic character. Beyond these striking examples, this work opens up opportunities to describe any electronic properties that depend only on subparts of the density in atoms, molecules, or solids.

What can tell the quantum chemical topology on carbon–astatine bonds?

ABSTRACT The nature of carbon–astatine bonds involved in some model species that mimic 211At-labelled biomolecules, was investigated by means of ELF and QTAIM analyses in a context of two-component relativistic computations. The nature of the bonded carbon atom proved to be decisive. When At is bonded to an ethynyl group, some charge delocalisation with the vicinal triple C–C bond strengthens the At–C bond and gives it a multiple bond character. However, At displays also a large positive charge which may alter the in vivo stability of such At–C bonds. In the case of an isopropyl group, the At–C bond is less polarised but also much weaker. In contrast, the bond remains strong whilst retaining a small At positive charge when At is bonded to an sp2 carbon atom. Hence, these latter results rationalise why aromatic or aryl groups appear reasonably suited for a priori stable radiolabelling of biomolecules with 211At in the context of alpha therapy.

Understanding phase transition in the ZnSiP 2 chalcopyrite, a quantum chemical topology study

Understanding the behavior of the matter under pressure is crucial for the development of novel polymorph of the chalcopyrite compound. Herein, we study the evolution of the bonding of ZnSiP2 up to 100xa0GPa. We particularize our results by means of the detailed ab initio study of its structural and dynamical properties. In fact, the compound shows disordered structure at 32xa0GPa which transforms at 82xa0GPa to a denser ordered one with eightfolds coordination. We show how the electron localization function can be useful to modulate the effect of compression along the proposed transition path. The integration of basin attractor reveals that the breaking of Si–P bonds is the key of formation of denser SiP8 units at high pressure.

The bonding picture in hypervalent XF3 (X = Cl, Br, I, At) fluorides revisited with quantum chemical topology

Hypervalent XF3 (Xu2009=u2009Cl, Br, I, At) fluorides exhibit T‐shaped C2V equilibrium structures with the heavier of them, AtF3, also revealing an almost isoenergetic planar D3h structure. Factors explaining this behavior based on simple “chemical intuition” are currently missing. In this work, we combine non‐relativistic (ClF3), scalar‐relativistic and two‐component (Xu2009=u2009Bru2009−u2009At) density functional theory calculations, and bonding analyses based on the electron localization function and the quantum theory of atoms in molecules. Typical signatures of charge‐shift bonding have been identified at the bent T‐shaped structures of ClF3 and BrF3, while the bonds of the other structures exhibit a dominant ionic character. With the aim of explaining the D3h structure of AtF3, we extend the multipole expansion analysis to the framework of two‐component single‐reference calculations. This methodological advance enables us to rationalize the relative stability of the T‐shaped C2v and the planar D3h structures: the Coulomb repulsions between the two lone‐pairs of the central atom and between each lone‐pair and each fluorine ligand are found significantly larger at the D3h structures than at the C2v ones for Xu2009=u2009Clu2009−u2009I, but not with Xu2009=u2009At. This comes with the increasing stabilization, along the XF3 series, of the planar D3h structure with respect to the global T‐shaped C2v minima. Hence, we show that the careful use of principles that are at the heart of the valence shell electron pair repulsion model provides reasonable justifications for stable planar D3h structures in AX3E2 systems.