Even if a high-level method like CCSD(T) or a very accurate XC functional is used in atomistic simulations, still a comparison to real world experimental observations might not be straightforward. One reason is that, most commonly, gas phase molecules are represented by modelling only a single static instance of the molecule. However, this assumption might only be correct at 0 K, since, at higher temperatures, vibrations and rotations will change the structure. To address this problem, statistical effects have been appreciated in high-pressure experimental/computational studies early on. Another aspect, which has recently been discussed, e.g., in the field of conceptual density function theory, is the inclusion of external electronic or magnetic fields to the simulations to mimic experimental conditions. The main reason why it is often difficult to compare the outcomes of experiments and calculations is the computational resources that are available nowadays. Therefore, the need of experimental model studies that can be compared to theoretical calculations is crucial. In the context of heterogeneous catalysis, Sauer and Freund discussed the benefit of such model studies to identify factors that determine the properties of catalytic materials with respect to reactions by systematically increasing the complexity of the system. Similar approaches are needed and used in the context of high pressure research. One example is a study of McWilliams et al., who investigated processes in planetary interiors in an experimental model study of phase transitions of MgO, which is abundant on terrestrial planets. The same system has then been investigated by Holmström and Stixrude with first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O. Synergistic efforts like these enable refinements of the simulation techniques and make a crucial contribution towards increasing their reliability.