The second-order Moller-Plesset limit for the barrier to linearity of water

A series of high-quality conventional and explicitly correlated second-orde r Moller-Plesset energies, denoted as MP2 and MP2-R12/A, respectively, was computed in a state-of-the-art attempt to arrive at the ab initio limit for the barrier to linearity of water. [O/H]-centered Gaussian basis sets as l arge as [19s13p11d9f7g5h3i/13s11p9d7f5g3h] were employed in the study. We f ind that basis functions with high orbital angular momentum quantum number (h and i) are important for highly accurate predictions of the electronic e nergy, even when explicitly correlated approaches are utilized. This observ ation is at variance with previous claims that explicitly correlated method s require basis sets saturated only to the level of f functions for spectro scopic accuracy. Our best explicitly computed value for the MP2 contributio n to the barrier is -357 cm(-1). The resulting final ab initio estimate for the classical barrier to linearity of water is 11 119 +/- 15 cm(-1), in go od agreement with the most recently obtained empirical value of 11 105 +/-5 cm(-1). (C) 2001 American Institute of Physics.