Noticias / IMIT brilla en la conferencia internacional REHE 2024 con destacadas presentaciones.

NOTICIA INSTITUCIONAL

IMIT brilla en la conferencia internacional REHE 2024 con destacadas presentaciones.

El Instituto de Modelado e Innovación Tecnológica (IMIT) tuvo una destacada participación en la 14ª Conferencia Internacional sobre Efectos Relativistas en Química y Física de Elementos Pesados (REHE 2024), celebrada del 7 al 11 de octubre de 2024 en Amersfoort, Países Bajos. Investigadores del IMIT presentaron tres trabajos que exploran las fronteras de la física teórica y la química cuántica relativista.

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14ª Conferencia Internacional sobre Efectos Relativistas en Química y Física de Elementos Pesados (REHE 2024)

Expositor: Dr. Agustín Aucar

Título: Role of spin-orbit effects in the formal connection between NMR shielding and nuclear spin-rotation tensors

Resumen:

El Dr. Agustín Aucar presentó una innovadora teoría relativista que generaliza la conexión entre el apantallamiento magnético nuclear y las constantes de "espín nuclear - rotación molecular", superando las limitaciones del modelo tradicional de Ramsey y Flygare para moléculas con elementos pesados. Su trabajo, que incluye la implementación de un código computacional para el modelado, analiza el rol crucial de los efectos de espín-órbita en esta nueva relación. Además, demostró la validez de la teoría en el marco de la electrodinámica cuántica (QED) y su alta precisión para describir las contribuciones que violan la simetría de paridad, provenientes de interacciones electrodébiles.

Título: A new field theory for expressing relativistic polarization propagators as bosonic propagators

Autores: Lic. Mariano T. Colombo Jofre & Dr. Gustavo A. Aucar

Resumen:

Se presentaron avances en la teoría de propagadores de polarización, introduciendo el concepto de "campo de excitación" para describir transiciones electrónicas en sistemas atómicos y moleculares. Su enfoque, basado en la teoría cuántica de campos, establece una equivalencia entre excitaciones electrónicas y bosones virtuales. Al aplicar la definición del propagador de Feynman a este campo, se obtienen expresiones para los propagadores de polarización. Este marco teórico ofrece nuevas posibilidades para incluir correcciones radiativas de la QED en el cálculo de parámetros de RMN y explorar conexiones con la mecánica estadística y el entrelazamiento cuántico.

Título: New insights on the spin-dependent and time-reversal dependent electronic mechanisms underlying the NMR spectroscopic parameters

Autores: Lic.Brisa Ramirez, Lic. Daniel Bajac & Dr. Gustavo A. Aucar

Resumen:

Se abordó la descripción de los mecanismos electrónicos que determinan los parámetros espectroscópicos de RMN en el marco relativista. Dado que el espín no es un buen número cuántico en relatividad, proponen un enfoque basado en la dependencia de la reversibilidad temporal, utilizando operadores restringidos de Kramers. Presentaron el formalismo general y aplicaciones de la teoría de propagadores de polarización relativista con bases de pseudo-espín. Se exploraron los mecanismos electrónicos tipo singlete y triplete para los acoplamientos J de RMN y se presentaron resultados para SnXH3 (X=Br, I). Este trabajo es un paso hacia la inclusión de la simetría CPT en las bases de operadores.

Título: Probable Correlation Between Molecular Parity Violation Energy and an Electronic Measure of Chirality
Autores: Juan J. Aucar, Alessandro Stroppa & Gustavo A. Aucar

Abstract:
Chirality is an ever-relevant topic in physics. A chiral molecule and its enantiomer (the isomer obtained by spatial reflection) should be exactly equivalent from an energetic point of view if parity were conserved. However, when considering weak forces that produce parity violation effects, a very small energy difference ΔEPV is obtained between the two enantiomers, which may be considered as one of the cornerstones to understanding the evolution of biological homochirality. In this study, we focus on the electronic measure of chirality (ECM) as a suitable descriptor to quantify the level of chirality of a given molecule. We calculated the ECM in a representative set of chiral molecules as well as their ΔEPV values within a four-component relativistic framework applying ab initio methods. Our results show a novel, strong, and positive correlation between ECM and ΔEPV, from which the existence of a subtle interaction between the weak forces acting within the nuclei of a chiral molecule and its chirality is inferred. These results also suggest that experimental investigations for the detection of parity violation in molecules should consider those with large ECM values.

Título: Electric Field Gradient within High-Order LRESC Formalism
Autores: Juan J. Aucar, Juan I. Melo & Alejandro F. Maldonado
Abstract:
We present a comprehensive analysis of the relativistic corrections to the electric field gradient (EFG) using the Linear response with the elimination of the small component (LRESC) scheme. Originally developed for magnetic shielding constants, LRESC has recently been extended to EFG calculations. We explored the methodology up to 1/c⁴ order and recently introduced the spin-dependent corrections for the first time. Notably, up to the first order (1/c²), there are no virtual pair contributions, with such contributions and triplet corrections only arising at the second order (1/c⁴). LRESC was applied to the study of various benchmark systems, including hydrogen halides HX (X = F, Cl, Br, I, At), XZY bi-linear molecules (Z = Zn, Cd, Hg; X, Y = F, Cl, Br, I, At), dihalogens XY (X, Y = F, Cl, Br, I, At), and chiral molecules CHClFX (X = Br, I, At). The results indicate that LRESC provides a close approximation to relativistic four-component calculations at Dirac–Hartree–Fock (4c-DHF) as well as Density functional theory levels (4c-DFT), even for heavy atoms such as At and Hg. The inclusion of high-order (1/c⁴) spin-dependent terms further refines LRESC's accuracy, yielding differences of less than 1% from 4c-DHF values. Additionally, LRESC reproduces precisely correlation effects at DFT level, which are non-additive with respect to relativist effects. The method also shows promise for nuclear quadrupole coupling constant (NQCC) calculations, aligning closely with experimental data. This study highlights the robustness of the LRESC performance in accounting for relativistic effects in EFG calculations of heavy-atom-containing molecules. Recently we have shown that the LRESC scheme is easily applicable to large chiral and tetrahedral systems containing heavy nuclei, and it may be applied to other related chiral molecules that can be suitable for experiments that aim to detect PV effects.

Título: Parity-violation effects on NMR shielding tensors of MX (M=Ga, In, Tl; X=F, Cl, Br, I, At) molecules
Autores: Javier Martinez, I. Agustín Aucar, Konstantin Gaul, Karol Koziol, Robert Berger & Gustavo A. Aucar
Abstract:
The TlF molecule is considered to be important in searching for parity-violation (PV) effects on NMR spectroscopic parameters (the indirect J-coupling tensor and the nuclear magnetic shielding tensor, σ) by theory or experiments. Recently we have been working on the calculation and the analysis of relativistic and QED effects on NMR shielding constants of TlX (X=F, Cl, Br, I, At) molecules. We found some patterns that explain the behavior for both effects, i.e. relativistic and QED. In this communication, we shall show the latest results of the calculations, within the framework of relativistic polarization propagators, of the order of magnitude and the electronic origin of the NMR shieldings of the set of molecules mentioned in the title. We found a well-defined pattern for the
dependence of σ^PV ( X ) with the nuclear charge of X and the frontier molecular orbitals (MOs). We analyze the main shielding pathways (virtual MO excitations giving the largest contributions to the shielding) and the behavior of the parity-conserving and the parity-violation contributions to the shieldings.

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