Not Just Another Crystal Field Software.

This manuscript presents NJA-CFS, a Python-based comprehensive toolkit for crystal field/ligand field calculations. NJA-CFS is designed to perform simulations of electronic structure properties, including the magnetic ones, for transition metals and lanthanoid complexes, giving access to several CF/LF parametrization schemes, from point-charge model and AOM to AILFT parameters, putting great effort in the implementation of routines for CF parameters manipulation and rotation. NJA-CFS was designed to meet the needs of both first-time users of crystal field theory and those who require a high degree of flexibility in the choice of crystal field parameters formalisms. In this manuscript, we present the theoretical foundations of the program routines and the comparison of NJA-CFS calculation results either to experimental data or ab initio computations, proving the advantages that access to multiple CFPs formalism can bring in. We also present intuitive applications of the NJA-CFS routines to didactically valuable examples, like the projection of CF/LF splitting on real d- and f- orbitals and the calculations of Tanabe-Sugano diagrams for arbitrary symmetries and with the inclusion of spin-orbit coupling.