Benchmark calculations on nucleobases: uracil as a test case

The uracil molecule has been chosen as a test case for benchmark calculations in order to test how far it is possible to go in extrapolation procedures at the coupled cluster level for nucleobases. The coupled-cluster level of theory with single and double excitations, and a quasiperturbative account for triples substitutions [CCSD(T)] has been mainly considered. With respect to the single molecule, its equilibrium geometry has been optimized at the CCSD(T)/cc-pVTZ level in the frozen core approximation, whereas its energy has been extrapolated to the complete basis set (CBS) limit also accounting for core correlation corrections. The harmonic force field has been computed employing the second-order Moller-Plesset perturbation theory (MP2) in conjunction with the core-valence cc-pwCVTZ basis set correlating all electrons. The face-to-face π-stacked dimer has also been considered. The intermonomer distance has been optimized at the CCSD(T)/cc-pVTZ level of theory in the frozen core approximation, whereas its energy has again been extrapolated to the CBS limit also accounting for core correlation corrections. In conclusion, it will be shown that the results available in the literature for DNA base pairs, amino acid pairs and model complexes can be improved.