A CCSD(T)-R12 STUDY OF THE 10-ELECTRON SYSTEMS NE, F-, HF, H2O, NH3, NH4+ AND CH4

Explicitly correlated coupled-cluster methods with linear r(ij) terms up to the CCSD(T)-R12 method are applied to the ground states of the N e atom, the F-ion and the molecules HF, H2O, NH3, NH4+, CH4 in their e quilibrium geometries, and to NH3 also in its planar conformer. Result s close to the basis set limit are obtained on MP2, MP3, MP4, CCSD, CC SD[T] and CCSD(T) level. The CCSD(T)-R12 results for the total energy agree with the estimated experimental non-relativistic energies within the limits of accuracy of the latter.