The g 1-x-y-1 energy functions for each molecular building block are presented in Figure . Each energy function is generated by publicly available code [Ref. 32]. The thinner, patterned lines in Figure represent the component functions f 1-x-y-1 that contribute to g 1-x-y-1 . The plot of g 1-2-2-1 for the butane building block looks very similar to that of the g 1-3-3-1 for 2,3-dimethylbutane as each has one global minimum, two local minima, two local maxima, and one global maximum. By contrast, the g 1-4-2-1 , g 1-4-3-1 and g 1-4-4-1 energy functions all have three global minima and three global maxima. This is due in part to the tetrahedral structure of sp 3 hybridized carbon bonds and the rotational symmetry of the internal bond.