Van der Waals Interactions in Pyridine and Pyridine-like Molecular Crystals: An \textit{ab initio} Molecular Dynamics Study

Pyridine has recently been investigated as a potentially effective material for use in artificial light harvesting.\footnote{ EB Cole, PS Lakkaraju, DM Rampulla, AJ Morris, E Abelev, AB Bocarsly J. Am. Chem. Soc., \textbf{132}, 11539 (2010).} In this work, we propose the use of \textit{ab initio} molecular dynamics (AIMD) to gain valuable physical insight into the artificial photosynthetic processes occurring in condensed-phase pyridine, the study of which has been limited to semi-empirical force fields to date.\footnote{AT Anghel, GM Day, SL Price CrystEngComm., \textbf{4}, 348 (2002).} For this purpose, we introduce an accurate and efficient AIMD method, based on density functional theory (DFT) and a self-consistent pairwise description of van der Waals (vdW) interactions, for use in finite temperature and pressure (NPT) simulations on pyridine and several pyridine-like molecular crystals (PLMCs). Utilizing this approach, we demonstrate that vdW forces play a crucial role in the theoretical prediction of the structure and density of pyridine and PLMCs, and therefore must be accounted for in studies of these potential alternative energy materials.