The starting structures were obtained in a manner similar to that used for the SAMPL8 reference calculations , by docking guests to the host using OEDock with the Chemgauss4 scoring function from the OpenEye Toolkits (release 2019.10.2). To compare general force fields, the bonded and initial Lennard-Jones parameters were obtained from GAFF2 as implemented in Antechamber , or assigned based on OpenFF v1.2.0 71 or v2.0.0 72 using openff-toolkit release v0.10.1. Each host guest system was solvated with 2500 TIP3P water molecules in a rectangular box whose dimensions were approximately 40 x 40 x 63 cubic Å. Sodium or chloride counterions with parameters from Joung and Cheatham were added as needed to neutralize each host-guest system, and additional sodium and chloride ions were added to match experimental ionic strength. AM1BCC partial atomic charges for hosts and guests were generated with oequacpac (with function oequacpac.OEAssignCharges(mol, oequacpa.OEAM1BCCCharges())) as implemented with OpenEye Toolkits.