Communications in Physics

Structural prediction of carbon cluster isomers with machine-learning potential

Duy Huy Nguyen — Tue, 11 Jun 2024 00:00:00 +0700

Structural prediction of low-energy isomers of carbon twelve-atom clusters is carried out using the recently developed machine-learning potential GAP-20. The GAP-20 agrees with density-functional theory calculations regarding geometric structures and average C-C bond lengths for most isomers. However, the GAP-20 substantially lowers the energies of cage-like structures, resulting in a wrong ground state. A comparison of the cohesive energies with the density-functional theory points out that the GAP-20 only gives good results for monocyclic rings. Two multicyclic rings appear as new low-energy isomers, which have yet to be discovered in previous research.

Hybridization of an s-wave impurity with graphene lattice

Hoa T. M. Nghiem, Tien-Lam Pham, Ngoc-Linh Nguyen, Hung T. Dang — Tue, 11 Jun 2024 00:00:00 +0700

Hybridization function is a quantity characterizing electron hoppings between an impurity and a host material in which the impurity resides, a full understandinging of it is crucial for studying correlation effects in various impurity problems. This work studies the hybridization function for the Anderson impurity model describing a single-orbital impurity on a honeycomb lattice simulating graphene and presents a calculation approach to obtain this function at low energy. Within this approach, the general form of the hybridization function in graphene is presented and analytical expressions of low-energy hybridization spectrum are obtained. The results quantitatively match numerical solutions for different impurity positions on the lattice. The effect of the low-energy hybridization spectrum and the capability to predict the correlated effects of the impurity problem are discussed thoroughly, suggesting that different types of pseudogap Kondo effect may occur at different impurity positions.

Dirac CP violation phase in the neutrino sector with A4 flavour symmetry

Phi Quang Van, Nguyen Anh Ky, Tien Manh Tran — Tue, 11 Jun 2024 00:00:00 +0700

CP violation is one of the problems of the physics beyond the Standard Model. It can happen in both the quark and the lepton sectors. In the present paper, following the work arXiv:1602.07437 [hep-ph], this problem is re-considered in the lepton sector (neutrino subsector) within an extended Standard Model with an $A_4$ flavour discrete symmetry with a new and more convenient parametrization. As a result, a perturbative mixing matrix is derived. Then, the Dirac CP violation phase $\delta_{CP}\equiv \delta$ and the Jarlskog invariant $J_{CP}\equiv J$ are analytically obtained from theoretically derived equations leading to the solutions $\delta= \pm {1\over 2}\pi$ . Between the two solutions, the solution $\delta=-{1\over 2}\pi$ (i.e., ${3\over 2}\pi$) is more preferable as it is more consistent with the experimental data for the inverted ordering of the neutrino masses for the gobal fit [PDG] or the normal ordering [T2K, NO$\nu$A]). A relation between $\delta$ and $J$ is also given in terms of new parameters. The maximum value of Jarlskog invariant $|J^{max}|$ is found in the range $0.0237 < |J^{max}| < 0.034$, covering the 2022-2023 global fit values [PDG]: $|J_{PDG}^{max}|= 0.0336\pm 0.0006 ~(\pm 0.0019)$ at $1\sigma ~(3\sigma$). Other values of J can be determined by the ralation $J (\delta)$ and approximated by Fig. 2. between two solutions.