Exploring Caffeine-Phenol Interactions by the Inseparable Duet of Experimental and Theoretical Data.

Intermolecular interactions are difficult to model, especially in systems formed by multiple interactions. Such is the case of caffeine-phenol. Structural data has been extracted by using mass-resolved excitation spectroscopy and double resonance techniques. Then the predictions of seven different computational methods have been explored to discover structural and energetic discrepancies between them that may even result in different assignments of the system. The results presented herein highlight the difficulty of constructing functionals to model systems with several competing interactions, and raise awareness of problems with assignments of complex systems with limited experimental information that rely exclusively on energetic data.