IMIT shines at REHE 2024 international conference with standout presentations.

Speaker: Dr. Agustín Aucar

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

Abstract:

Dr. Agustín Aucar presented an innovative relativistic theory that generalizes the connection between nuclear magnetic shielding and "nuclear spin - molecular rotation" constants, overcoming the limitations of the traditional Ramsey-Flygare model for molecules with heavy elements. His work, which includes the implementation of a computational code for modeling, analyzes the crucial role of spin-orbit effects in this new relationship. In addition, he demonstrated the validity of the theory in the framework of quantum electrodynamics (QED) and its high accuracy in describing parity symmetry-violating contributions from electroweak interactions.

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

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

Abstract:

Advances in the theory of polarization propagators were presented, introducing the concept of "excitation field" to describe electronic transitions in atomic and molecular systems. Their approach, based on quantum field theory, establishes an equivalence between electronic excitations and virtual bosons. By applying the definition of the Feynman propagator to this field, expressions for polarization propagators are obtained. This theoretical framework offers new possibilities to include radiative corrections of QED in the calculation of NMR parameters and to explore connections with statistical mechanics and quantum entanglement.

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

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

Abstract:

The description of the electronic mechanisms that determine the NMR spectroscopic parameters in the relativistic framework was addressed. Since spin is not a good quantum number in relativity, they propose an approach based on the time-reversibility dependence, using restricted Kramers operators. They presented the general formalism and applications of the relativistic polarization propagator theory with pseudo-spin bases. Singlet and triplet electronic mechanisms for NMR J couplings were explored and results for SnXH3 (X=Br, I) were presented. This work is a step towards the inclusion of CPT symmetry in operator bases.

Título: Probable Correlation Between Molecular Parity Violation Energy and an Electronic Measure of Chirality
Authors: 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
Authors: 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.

Title: Parity-violation effects on NMR shielding tensors of MX (M=Ga, In, Tl; X=F, Cl, Br, I, At) molecules
Authors: 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.