A flexible-monomer two-body potential energy function was developed that approaches the high level CCSD(T)/CBS potential energy surface (PES) of carbon dioxide (CO ) systems. This function was generated by fitting the electronic energies of unique CO monomers and dimers to permutationally invariant polynomials. More than 200,000 CO configurations were used to train the potential function. Comparisons of the PESs of six orientations of flexible CO dimers were evaluated to demonstrate the accuracy of the potential. Furthermore, the potential function was used to determine the minimum energy structures of CO clusters containing as many as 13 molecules. For isomers of (CO ) , the potential demonstrated energetic agreement with the M06-2X functional and structural agreement of the B2PLYP-D functional at substantially reduced computational costs. A separate function, fit to MP2/aug-cc-pVDZ reference energies, was developed to directly compare the two-body potential to the ab initio MP2 level of theory. © 2017 Wiley Periodicals, Inc.