With the sublevelset persistence for the building block energy functions g 1-x-y-1 : S 1 → R established (Figures and), we next pursue the sublevelset persistence for more complex molecules. A simplifying approximation is made that g w-x-y-z does not depend on the degrees of the terminal C-atoms. Consider 2-methylpentane (Figure ), whose conformational potential energy function V is a combination of 1-2-2-3 and 1-3-2-2 molecular building blocks. Within this approximation, V : (S 1 ) 2 → R has the contribution from the 1-3-2-2 replaced by a 1-3-2-1 potential, and the 1-2-2-3 function replaced by 1-2-2-1. Hence the PEL for 2-methylpentane, using the energy landscape formulas from Ref. 31 and Eqn. 2 is (using the coefficients from Table ):