Allowing any of the zeroth-order XC coefficients a 0 , b 0 , c 0 and d 0 (refer to Equation ) to be different than zero significantly compromises the accuracy of our model, especially for low-energy interaction configurations. However, setting these zeroth-order coefficients to zero ensures that our model closely resembles the naïve model for large interatomic distances. This is a desirable feature since, at considerable distances between interacting molecules, the naïve model approximates the exact answer due to the negligible correlation between the electrons of each molecule. Moreover, by constraining the other XC coefficients to exact expression as shown in Equations 20a through 20d, and then minimizing the coefficients of these expressions with respect to our reference data, rather than having each XC coefficients as a minimization variable, eliminates undesired oscillations at short interatomic distances.