The symbols X i in equations 1 and 2 denote the reference X values of all 4 states involved in CO 2 chemisorption in liquid amines. Each of the 3 components of vectors X i was determined from equilibrium MD simulations of unbound CO 2 , zwitterion and carbamate in liquid ammonia. The predefined values of vectors X i are given in the SI. The constant λ defines the smoothness of both S and Z variables, and it is here set to 12.