Wednesday, 4 November 2026: 0 new papers, 3 cross-lists and 0 replacements in Atomic and Molecular Clusters (physics.atm-clus), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
Charge equilibration assigns atomic charges by equalizing an atomic chemical potential built from electronegativity, hardness and the Coulomb interaction. Under one global constraint it lets charge flow without limit between molecules, which fluctuating-charge models prevent with one neutrality constraint per molecule. A metal needs the opposite: a global constraint and a hardness near zero, and there the charge operator becomes indefinite unless it includes each charge's own self-energy. Here, we present samQEq (solids-and-molecules QEq), a unified charge-equilibration package for LAMMPS that combines the two constructions in one energy functional and one matrix-free solve. An orthogonal projector imposes one neutrality constraint per molecule, and the finite-width self-energy of a Gaussian charge on designated conductor types, narrower than the conductor's own Gaussian, keeps the conductor's part of the operator positive definite at any hardness. On a gold slab carrying a water film, the operator stays definite down to the conductor limit of the model, the metal screens a point charge by a constant amount at every height beyond 4 {\AA}, and the film's charges stay bounded under dynamics. Reciprocal-space electrostatics is evaluated inside the matrix-vector product, and three distinct shielding kernels are run-time settings. We verify the implementation by reproducing a published fluctuating-charge water model without refitting, and the native ReaxFF charge-equilibration step to approximately $10^{-9}\,e$. On a single four-V100 node the largest tested systems run at approximately twice the throughput of a 128-core CPU node. samQEq thus provides one charge-equilibration layer for molecules, conductors and the interfaces between them.
We present a two-dimensional axisymmetric physics-informed neural network (PINN) of the discharge channel of the P5 Hall thruster at 300 V and 5.4 A, which solves eleven coupled plasma fields and assimilates 145 internal probe measurements per field reconstructed from the data of Haas and Gallimore. The electric potential is obtained from Poisson's equation in charge-separation form, n_e = n_i(1+eta), with eta bounded by construction, which keeps the stiff electrostatic constraint active and trainable. The reference solution agrees with the training profiles to relative L2 errors of 0.017, 0.073 and 0.205 for the potential, electron temperature and ion density, and held-out tests show the potential to be far more robust than the ion density to the withdrawal of measurement lines. We then test the solution against requirements the data fit does not reveal: global particle and current balances, the electron current implied by the momentum equation, the field-aligned electron force balance and the axial ion momentum budget. These expose a neutral inflow six times the measured flow, a bound in the potential representation, and a momentum-implied electron current, more than 99% field-aligned, exceeding the discharge current by orders of magnitude. Correcting these, with a divergence-free magnetic field fitted to measured data, uncertainty-weighted data, the electron pressure gradient and progressively imposed field-aligned and current constraints, yields a solution that conserves particles to within 3%, holds the current between 5.1 and 5.4 A and places 97% of the potential and 88% of the temperature measurements within their uncertainties. Within the tested single-velocity fluid formulation, however, the ion density, potential and ion velocity could not be matched together, and the field-aligned electron balance remains the main obstacle to electron self-consistency.
We study the one- and two-boson energy subspaces of finite open Bose--Hubbard chains with Fibonacci-modulated hopping and zero on-site potential. Their spectra exhibit a hierarchy of bands and gaps, and a critical zero-energy mode for odd lengths, in agreement with prior research. For the singe-excitation subspace we find two families of length-invariant finite-energy states localized at the left cluster boundary. For the two-boson subspace, we report both doublon and separated-pair excitations in the form of Tamm/Shockley states localized near either end. In particular, the right-edge doublon states occur across all Fibonacci generations whereas the left-side states appear every second generation. We check numerically that the second-order perturbation theory accounts well for the structure of the spectrum and the edge states in the doublon subspace in the strong-coupling regime. The results are useful for future explorations of many-body physics beyond numerical tractability, specifically using near-term Josephson quantum simulators.