arXiv subjects

Jorge Charry

Publications and source records attributed to Jorge Charry.

4 recordsLinked to original sources

arXiv2026

Two Protons, Two Positrons, and Four Electrons: Covalent Bond with van der Waals Characteristics

Classifying interactions is key in the physical sciences, and bonding mechanisms in matter-antimatter systems remain particularly enigmatic. Here we focus on a paradigmatic example of positronium hydride (PsH) dimer composed of two protons, two positrons, and four electrons, whose bonding nature has been previously described as either ionic, covalent, or van der Waals-like. Accurate quantum Monte Carlo calculations show that the two positrons occupy a delocalized molecular orbital that envelopes the two hydrogen anions and responds as a collective dipole to an applied electric field. This positronic bonding stems from quantum correlations that resemble a single covalent bond formed between negatively charged pseudo-nuclei, but with a bond strength commensurate with the traditional van der Waals interaction. Our findings suggest that the ability to form delocalized proto-bonds is a more general property of quantum systems, and could be present in a broader class of particles, antiparticles, and quasi-particles interacting with matter.

physics.chem-ph↗

arXiv2025

QMeCha: quantum Monte Carlo package for fermions in embedding environments

We present the first open access version of the QMeCha (Quantum MeCha) code, a quantum Monte Carlo (QMC) package developed to study many-body interactions between different types of quantum particles, with a modular and easy-to-expand structure. The present code has been built to solve the Hamiltonian of a system that can include nuclei and fermions of different mass and charge, e.g. electrons and positrons, embedded in an environment of classical charges and quantum Drude oscillators. To approximate the ground state of this many-particle operator, the code features different wavefunctions. For the fermionic particles, beyond the traditional Slater determinant, QMeCha also includes Geminal functions such as the Pfaffian, and presents different types of explicit correlation terms in the Jastrow factors. The classical point charges and quantum Drude oscillators, described through different variational ans\"atze, are used to model a molecular environment capable of explicitly describing dispersion, polarization, and electrostatic effects experienced by the nuclear and fermionic subsystem. To integrate these wavefunctions, efficient variational Monte Carlo and diffusion Monte Carlo protocols have been developed, together with a robust wavefunction optimization procedure that features correlated sampling.

physics.chem-ph↗

arXiv2022

The three-center two-positron bond

Computational studies have shown that one or more positrons can stabilize two repelling atomic anions through the formation of two-center positronic bonds. In the present work, we study the energetic stability of a system containing two positrons and three hydride anions, namely 2\ce{e^+[H^{3-}_3]}. To this aim, we performed a preliminary scan of the potential energy surface of the system with both electrons and positron in a spin singlet state, with a multi-component MP2 method, that was further refined with variational and diffusion Monte Carlo calculations, and confirmed an equilibrium geometry with \ce{D_${3h}$} symmetry. The local stability of 2\ce{e^+[H^{3-}_3]} is demonstrated by analyzing the vertical detachment and adiabatic energy dissociation channels. Bonding properties of the positronic compound, such as the equilibrium interatomic distances, force constants, dissociation energies, and bonding densities are compared with those of the purely electronic \ce{H^+_3} and \ce{Li^+_3} systems. Through this analysis, we find compelling similarities between the 2\ce{e^+[H^{3-}_3]} compound and the trilithium cation. Our results strongly point out the formation of a non-electronic three-center two-positron bond, analogous to the well known three-center two-electron counterparts, which is fundamentally distinct from the two-center two-positron bond [D. Bressanini, \textit{J. Chem. Phys.} \textbf{155}, 054306 (2021)], thus extending the concept of positron bonded molecules.

physics.chem-ph↗

arXiv2020

Four-Dimensional Scaling of Dipole Polarizability in Quantum Systems

Polarizability is a key response property of physical and chemical systems, which has an impact on intermolecular interactions, spectroscopic observables, and vacuum polarization. The calculation of polarizability for quantum systems involves an infinite sum over all excited (bound and continuum) states, concealing the physical interpretation of polarization mechanisms and complicating the derivation of efficient response models. Approximate expressions for the dipole polarizability, $\alpha$, rely on different scaling laws $\alpha \propto$ $R^3$, $R^4$, or $R^7$, for various definitions of the system radius $R$. Here, we consider a range of single-particle quantum systems of varying spatial dimensionality and having qualitatively different spectra, demonstrating that their polarizability follows a universal four-dimensional scaling law $\alpha = C (4 \mu q^2/\hbar^2)L^4$, where $\mu$ and $q$ are the (effective) particle mass and charge, $C$ is a dimensionless excitation-energy ratio, and the characteristic length $L$ is defined via the $\mathcal{L}^2$-norm of the position operator. %The applicability of this unified formula is demonstrated by accurately predicting the dipole polarizability of 36 atoms and 1641 small organic~molecules. This unified formula is also applicable to many-particle systems, as shown by} accurately predicting the dipole polarizability of 36 atoms, 1641 small organic \rrr{molecules, and Bloch electrons in periodic systems.

quant-ph↗