Density cumulant functional theory: first implementation and benchmark results for the DCFT-06 model

Density cumulant functional theory [W. Kutzelnigg, J. Chem. Phys. 125, 171101 (2006)] is implemented for the first time. Benchmark results are provided for atoms and diatomic molecules, demonstrating the performance of DCFT-06 for both nonbonded and bonded interactions. The results show that DCFT-06 appears to perform similarly to coupled cluster theory with single and double excitations (CCSD) in describing dispersion. For covalently bound systems, the physical properties predicted by DCFT-06 appear to be at least of CCSD quality around equilibrium geometries. The computational scaling of both DCFT-06 and CCSD is O(N(6)), but the former has reduced nonlinearities among the variables and a Hermitian energy functional, making it an attractive alternative.