SIMBA: A Python-based single-point astrochemical solver and analysis tool

Abstract

Determining molecular abundances in astrophysical environments is crucial for interpreting observational data and constraining physical conditions in these regions. Chemical modelling tools are essential for simulating the complex processes that govern molecular evolution. We present SIMBA, a new Python-based single-point astrochemical modelling package designed to solve chemical reaction networks across diverse astrophysical environments. The software follows standardised rate equation approaches to evolve molecular abundances under specified physical conditions, incorporating gas-phase chemistry, grain-surface processes, and photochemistry. While leveraging Python for accessibility, performance-critical routines utilise just-in-time compilation to achieve computational efficiency suitable for research applications. A key feature of SIMBA is its graphical interface, which enables rapid investigation of chemical evolution under varying physical conditions. This makes it particularly valuable for exploring parameter dependencies and complementing more computationally intensive multi-dimensional models. We demonstrate the package's capabilities by modelling chemical evolution in a photoevaporative flow driven by external FUV irradiation. Using simplified gas dynamics, we chain multiple SIMBA instances to create a dynamic 1D model where gas evolves both chemically and dynamically. Comparing this approach to typical static models - where chemistry in each grid cell evolves independently - reveals that molecular ices, especially those with relatively high binding energies like H2O, can survive much farther into the flow than static models predict. This example case highlights how SIMBA can be extended to higher dimensions for investigating complex chemical processes. The package is open-source and includes comprehensive documentation.