Advances in computational hardware have enabled the development of molecular dynamics (MD) simulations capable of thoroughly sampling a protein's conformational landscape at biologically relevant timescales. This technique relies on accurate descriptions of atomic forces as dictated by potential energy functions (force fields), which have been continuously improved by various groups over time through reparameterization against experimental measurements. A considerable challenge in force field validation is the computational cost of simulating protein folding equilibria, which requires extensive conformational sampling. Two main approaches have been used to simulate folding dynamics on long timescales. One approach, pioneered by D. E. Shaw Research, has been to develop a special-purpose computer called Anton to simulate single MD trajectories on timescales orders of magnitude longer than possible with general-purpose computing methods. 11 Extensive force field validation studies performed on Anton made it possible to perform long-timescale (0.1-1 ms) reversible folding trajectories for 12 fast-folding proteins, providing an invaluable benchmark for many subsquent studies. More recently, Robustelli et al. used Anton to benchmark the performance of six different force fields by comparing 21 simulated structured and disordered proteins against experimental NMR measurements. An alternative approach to conformational sampling is to simulate massively parallel numbers of MD trajectories using distributed computing platforms such as Folding@home or GPUGRID, 17 or adaptively through weighted ensemble approaches. These methods The small size of chignolin (10 residues) made it highly tractable for molecular simulation studies, and subsequent computational studies of this protein lead to some debate in determining the specific folding mechanism and stable states. One of the first simulation studies of chignolin was performed by Suenaga et al. Using all-atom MD with the AMBER99 force field in explicit solvent (TIP3P water ), they reported an extensive description of chignolin's folding and unfolding mechanism with an emphasis on understanding Tyr2-Trp9 hydrophobic interactions in hairpin formation. Satoh et al. performed multicanonical MD with AMBER99 and GB/SA implicit solvent to study the folding free energy landscape of chignolin. They reported a stable misfolded state, defined by non-native backbone interactions between Asp3O and Gly7N. In this misfolded state, one of the strands is "flipped", leading to a misregistered strand pair, and residues Tyr2 and Trp9 on opposite sides of the beta sheet.