Following scikit-learn, the next most highly cited work is the VASP software (Figure ). Indeed, the next five software libraries (VASP , pymatgen , Phonopy 25 , matminer , and AFLOW ) are generally used to calculate (VASP, Phonopy) or analyze (pymatgen, matminer, AFLOW) materials properties through density functional theory (DFT). The final software, OVITO , is also used to visualize simulation results The high presence these software libraries within the group of materials machine learning papers suggests that a large fraction of materials machine learning is being performed on simulation data. Analysis of top databases cited within MSE-ML papers (Figure ) supports this trend: all three databases (Materials Project 29 , OQMD , and AFLOWLib.org ) focus primarily on density functional theory generated data sets.