Simulations of p ‐ tert ‐Butylcalix[4]arene with Multiple Occupancies of Small Guest Molecules

Classical molecular dynamics simulations were used to study low‐density β 0 ‐phase p ‐ tert ‐butylcalix[4]arene inclusion compounds with multiple calix occupancies of xenon, carbon dioxide, methane, and hydrogen guest molecules with guest–host ratios ranging from 1:4 to 4:1. Custom parameterized force fields were used for the guests and the AMBER force field for the calixarene units was validated in our previous work ( Chem. Eur. J. 2006 , 12 , 5231). The inclusion energy and unit cell volume of the calixarene inclusion compound were determined for various guest occupancies and for occupancies greater than 1:1, strong guest–guest interaction effects are observed. The structure and energetics of the 2:1 CO 2 /β 0 ‐phase inclusion compound were compared to those of the low‐temperature 2:1 CO 2 /calixarene in which the guest molecules occupy both cage and interstitial sites.