COMPLAX: A Python Tool Package for Automated Microsolvation of Organic Molecules

Abstract Since the solvent choice drives organic reactivity, accurate computational modeling of explicit solute–solvent interactions remains crucial but preparation-intensive. We present COMPLAX, an open-source Python tool that automates the generation and optimization of targeted microsolvated clusters around highly localized active sites. Unlike unconstrained global optimizers, COMPLAX employs a rigid-core approach to preserve delicate solute geometries. To ensure unbiased spatial sampling, it couples a deterministic Fibonacci spherical lattice with three-dimensional rotational randomizations. Generated structures are refined via a two-stage xTB geometry optimization, utilizing a constrained pre-relaxation step to prevent unphysical solvent detachment. By automating conformer ranking and energy evaluations via a simple command-line interface, COMPLAX provides a reproducible, out-of-the-box solution for explicit microsolvation workflows.