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Over the past decade, the Python-based Simulations of Chemistry Framework (PySCF) has developed into a widely used open-source platform for electronic-structure theory and quantum chemical method development. This article reviews the major advances since the previous overview in 2020, covering new modules and methodology, infrastructure changes, and performance benchmarks.

Carbocations are key species in interstellar chemistry, providing entry points for building larger hydrocarbons. CH+ , and more recently, CH_3^+, have been detected. Other carbocations await detection to provide a comprehensive view of the astrochemical network that is at work in the interstellar medium. We search for CH_2^+ in objects in which CH_3^+ was detected and evaluate the most favorable conditions for detecting the elusive ̧htwo reactive cation. We calculated the CH_2^+ rotational and rovibrational transitions expected to contribute in the mid- to far-infrared, focusing on the lower-energy rovibrational levels. We then calculated CH_2^+ infrared emission spectra at different excitation temperatures and compared them to JWST spectra of the externally irradiated disk d203-506 in Orion, where rm CH^+ and rm CH_3^+ have already been detected. We used thermochemical models to predict the abundance and spatial morphology of CH_2^+ to better understand its nondetection. The comparison to JWST spectra allowed us to provide excitation-temperature-dependent upper limits to the excited column density. These are several times lower than those detected for CH+$ and CH_3^+ in their excited states. Based on model calculations for photodissociation regions and assuming similar excitation temperatures, the upper limit derived from observations and CH$_2^+ model spectrum is either slightly above or below the column density expected from models of photodissociation regions. We provide a list of tabulated transitions to allow the community to search for this carbocation in future observations as CH_2^+ is key in providing observational constraints on astrochemical models.

Minimum energy paths of the eight lowest diabatic (bottom) and adiabatic (top) A′ and A″ electronic states of CH ₂ ⁺ for non-adiabatic dynamics.

This study reports the synthesis and characterization of anion exchange membranes (AEMs) tailored for application in alkaline water electrolysis for green hydrogen production. Novel membranes were developed by crosslinking polybenzimidazole (PBI) and poly(vinylbenzyl chloride) (PVBC) in a 1:2 ratio, followed by quaternization with either 1,4-diazabicyclo[2.2.2]octane (DABCO) or 1-methylpyrrolidine (MPY). Their performance was benchmarked against commercial membranes, including Fumasep® FAA-3-50 and Dapozol M-40. The membranes were thoroughly characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy, infrared and Raman spectroscopies, ionic conductivity, ion exchange capacity, water uptake and swelling measurements. Additionally, molecular dynamics simulations were performed to determine the diffusion coefficients of OH- and H2, providing further insight into ion transport and gas permeability at the molecular level. Electrochemical performance was evaluated in a flow-cell configuration under different pretreatment protocols. A key result of this work is the superior gas-barrier performance of the synthesized membranes. In stability electrolysis tests, both DABCO- and MPY-based membranes showed significantly reduced hydrogen crossover, 36% lower than FAA-3-50, decreasing from approximately 2.7% to just 1.7% H2 detected at the anode. This reduction in crossover is critical for enhancing efficiency and safety in hydrogen production. While FAA-3-50 delivered the best overall performance in short test activation conditions, the synthesized membranes demonstrated highly competitive performance and notable improvements in selectivity and stability. Dapozol M-40 was excluded from further analysis due to its poor electrochemical performance. These findings confirm the potential of tailored PBI/PVBC-based membranes for advanced alkaline electrolysis applications.

Following the previous study with an extensive range of quantum calculations involving different electronic states of the BN− anion [Dulitz et al., Phys. Scripta 100, 055411 (2025)], we now extend that work by modeling the quantum dynamics of the collision cooling of its rotational states in order to investigate possible paths for bringing this molecular anion down to temperatures of a few Kelvins. This specific ionic system is of direct interest when modeling experiments in cold ion traps where He or Ar atoms can function as the chief buffer gases that drive the anions down to the low trap temperatures. We employ accurate, ab initio calculations of the potential energy surfaces for the title system in its ground electronic state, interacting with either He or Ar atoms. We then obtain a wide range of inelastic cross sections and the ensuing rate coefficients in order to model the quantum kinetics of the time evolution of the cooling steps under different temperature and trap conditions. The results are analyzed and employed to estimate the cooling efficiency paths provided by various trap arrangements for the title anion. The results show that—using either of the two investigated species—the buffer gas cooling process very efficiently brings the anions to their lowest rotational states. These findings are very promising for future applications in the field of anion laser cooling.

Carbon hydrides play a crucial role in the formation of complex organic molecules in highly UV illuminated regions of the interstellar medium (ISM).

We investigate an optical cycling scheme for Doppler cooling cold trapped ¹¹B¹⁴N⁻ ions using transitions between the X ²Σ⁺ ground state and the B ²Σ⁺ excited state, and analyze here the relevant transitions for photon cycling and repumping. Our results show that slow population decay via the first excited electronic state A ²Π cannot be neglected. To improve the optical cycling efficiency, we consider additional transitions beyond what would be expected from the highly diagonal FranckCondon factor involving the B ²Σ⁺(v = 0) ← X ²Σ⁺(v = 0) transition. We estimate that the number of cycled photons alone is not likely to be sufficient to bring buffer-gas-cooled ¹¹B¹⁴N⁻ to temperatures near the Doppler cooling limit. Hence, pre-cooling, e.g., using a combination of cryogenic buffer gas and photodetachment cooling, will be essential to maximize the optical cycling efficiency and to reach a regime where Coulomb crystallization occurs. To explore pre-cooling with He or Ar buffer gases, we therefore also performed extensive quantum calculations of potential energy curves, transition moments and radiative rate coefficients for the BN⁻–buffer gas systems, to be implemented in a later study. Our results provide key insights for generating cold negative ions. These anions have, in fact, promising applications in various fields, ranging from quantum science and technology to fundamental physics and chemistry.

Context. In diffuse interstellar clouds, the excitation temperature derived from the lowest levels of H₃⁺ is systematically lower than that derived from H₂. The differences may be attributed to the lack of state-specific formation and destruction rates of H₃⁺, which are needed to thermalize the two species. Aims. In this work, we aim to investigate the possible influence of rotational excitation collisions of H₃⁺ with atomic hydrogen on its excitation temperature. Methods. We used a time-independent close-coupling method to calculate the state-to-state rate coefficients, incorporating a very accurate and full-dimensional potential energy surface recently developed for H₄⁺. We take a symmetric top approach to describe a frozen H₃⁺ as an equilateral triangle. Results. We derive rotational excitation collision rate coefficients of H₃⁺ with atomic hydrogen in a temperature range corresponding to diffuse interstellar conditions up to (J, K, ±) = (7, 6, +) and (J, K, ±) = (6, 4, +) for its ortho and para forms. This allows us to obtain a consistent set of collisional excitation rate coefficients and to improve on a previous study that included speculations regarding these contributions. Conclusions. The new state-specific inelastic H₃⁺ + H rate coefficients yield differences of up to 20% in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions on the excitation balance of H₃⁺, and that reactive H + H₃⁺ collisions are also needed to account for possible further ortho to para transitions.

We discuss the HCN + H⁻ reaction as a path to the formation of CN⁻, the smallest cyanopolyyne anion observed in several interstellar environments. We first obtain the new ab initio reactive potential energy surface using a full 5D representation, where only the C–N bond is kept fixed, and discuss the neural network procedure employed to yield an accurate fit for the dynamics. The reaction is then investigated by using a quasi-classical trajectory approach to scan the low-temperature range of the dark molecular clouds where the anion has been sighted. Calculations are extended to room temperature to make a successful comparison with existing experimental data. We further present reduced dimensionality modeling of the reaction as a 2D process within a variational-transition state treatment with the inclusion of long-range forces. The dominant role of such forces in producing large reaction rate coefficients is discussed for both treatments, which yield very similar sizes and behavior of such coefficients from 50 to 300 K. The implications of our results for the interstellar medium formation of the CN⁻ species via this chemical route are discussed, suggesting its greater significance over the radiative electron attachment paths, whose rate coefficients were found by recent calculations to be orders of magnitude smaller.