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A simple scheme is suggested to extrapolate the valence electron correlation to the one-electron complete-basis-set limit in species formed by atoms of hydrogen through neon. The performance of the novel scheme is benchmarked for the correlation energy with a data set of 106 systems and, for the polarizability, with 8 molecules. For the former, the results are excellent, most often better than when extrapolated with the best available two-parameter protocols. For the polarizability, they show an enhancement relative to the raw ab initio values, and good agreement with the experimental ones. [ABSTRACT FROM AUTHOR]

Abstract: The potential energy surface of exohedral HeC36 is analyzed in detail and extrapolated to the complete basis set limit using Møller-Plesset perturbation calculations. A limited number of coupled cluster singles and doubles calculations has also been performed. Exohedral complexes above the hexagonal faces toward the major axis are found to be the most stable, but the helium atom can move almost freely from the equator to the poles of C36 without dissociating the complex due to the disparity of masses. The effective 1D interaction potential has van der Waals attributes in good agreement with those estimated from He2 and a Girifalco function for the C36 dimer, supporting three bound states. [Copyright &y& Elsevier]

Abstract: A recently proposed scheme that enables a potential energy surface corresponding to a calculation with a large target basis set to be obtained from small basis set calculations via scaling of the electron correlation at a single-pivotal geometry is generalized to include an arbitrary number of such geometries. If the correlation is extrapolated to the complete basis set limit at the pivotal geometries and used for the scaling, the method can yield accurate potentials at costs up to factors nearly fifty times cheaper than required otherwise. The approach, free from parameters alien to the ab initio methods, is tested on N2, O2, and F2. [Copyright &y& Elsevier]

A potential energy surface is reported at the complete basis set limit for the ground electronic state of HO 2 + via a four dimensional interpolation in relaxed hyperspherical coordinates. The dissociated products OH + and O 2 + have also been studied at the complete basis set level and subsequently analytically modelled. In the case of O 2 + , the vibrational states predicted from the model potential have also been directly included in the fit. The potential form so obtained matches the RKR levels with a root mean square deviation below 1 cm - 1 . Spin orbit + relativistic effects have also been taken into account for the O 2 + ion. [ABSTRACT FROM AUTHOR]

The performance of various hierarchized basis sets has been assessed by extrapolating the correlation energy to the estimated one-electron complete basis set limit. New hierarchical numbers are obtained which are found to lie close to previously reported ones for the Dunning correlation-consistent basis. Universal hierarchical numbers are also suggested, with correlation extrapolations showing a significantly better performance than when based on traditional protocols. It is observed that the accuracy of the extrapolation is enhanced when the underlying plot approaches linearity. [ABSTRACT FROM AUTHOR]