High level coupled cluster determination of the structure, frequencies, and heat of formation of water.

The molecular structure, harmonic and anharmonic frequencies and atomization energy of the water monomer have been re-examined with high level electronic structure methods. We estimate the uncertainties in our final, best values as SigmaD(e)+/-0.09 kcal/mol, r(e)(OH)+/-0.000 05 A, [measured angle]HOH+/-0.007 degrees, (omega(i),nu(i))+/-0.2 cm(-1) (stretches), and +/-0.3 cm(-1) (bend). These findings serve as a useful benchmark for more approximate techniques, and a careful breakdown of the component pieces illustrates some of the difficulties encountered in trying to achieve tightly converged properties.