Small- and medium-core pseudopotentials representing [Ar]3d10- and [Kr]-like cores, respectively, have been adjusted for the In atom, supplementing the energy-consistent three-valence-electron large-core ([Kr]4d10 core) pseudopotential of the Stuttgart group. The performance of these potentials is tested against those of other groups and against experiment, in calculations for the ground-state potential curves of InH, InF, and InCl, both at the self-consistent-field and correlated levels. The role of the core size is discussed, and systematic errors of large- and medium-core pseudopotentials are analyzed.

Nonrelativistic and one-component relativistic energy-adjusted ab initio pseudopotentials for the noble gases neon through xenon are presented together with corresponding optimized valence basis sets. To account for nonscalar relativistic effects the relativistic pseudopotentials are supplemented with effective spin–orbit potentials. The reliability of the presented pseudopotentials is demonstrated in atomic test calculations on ionization potentials and spin–orbit splittings in comparison with nonrelativistic and relativistic all-electron calculations as well as experimental data. Together with extended valence basis sets the pseudopotentials are applied in calculations on the static dipole and quadrupole polarizabilities of the noble gas atoms. The best values, computed at the coupled-cluster level of theory [CCSD(T)], for the dipole and quadrupole polarizabilities of the noble gases are 2.69a30 and 7.52a50 for Ne, 11.07a30 and 52.25a50 for Ar, 17.06a30 and 97.39a50 for Kr, and 27.66a30 and 209.85a50 for Xe.

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Spectroscopic constants for InCl and InCl 3 are determined by a coupled cluster procedure using relatively large basis sets and an energy-consistent semilocal three valence electron pseudopotential for indium. Possible errors within the pseudopotential approximation are discussed in detail by comparison of available pseudopotentials adjusted through different techniques. Core-polarization corrections and the deviation from a point core approximation are discussed. These corrections, however, do not lead to more accurate bond distances as compared to the experimental results. Differently adjusted three valence electron pseudopotentials yield quite different results for the bond distances of InCl and InCl 3 . The single-electron adjusted energy-consistent pseudopotential of Igel-Mann et al. ͓Mol. Phys. 65, 1321 ͑1988͔͒ yields the best results and therefore, this pseudopotential has been chosen for all further investigations on molecular properties. The Dunham parameters for InCl are calculated by solving the vibrational-rotational Schrödinger equation numerically. A finite field technique is used to determine the dipole moment and dipole-polarizability of diatomic InCl. The dependence of several molecular properties on the vibrational quantum state is determined by calculating the expectation value P n ϭ͗n͉P(R)͉n͘, where P(R) is the distance dependent molecular property. The P(R) curves show strong linear behavior and therefore, the shape of the P n curve is mostly determined by anharmonicity effects in the InCl potential curve. For the vibrational ground state, ͉0͘, the calculated property P 0 deviates only slightly from the property determined directly at the equilibrium distance, P e . There is in general satisfying agreement of our calculated values with available experimental results. However, it is concluded that in order to obtain very accurate spectroscopic constants a small core definition for indium has to be preferred.

Systematic sequences of basis sets are used to calculate the spin-orbit splittings of the halogen atoms F, Cl, and Br in the framework of first-order perturbation theory with the Breit-Pauli operator and internally contracted configuration interaction wave functions. The effects of both higher angular momentum functions and the presence of tight functions are studied. By systematically converging the one-particle basis set, an unambiguous evaluation of the effects of correlating different numbers of electrons in the Cl treatment is carried out. Correlation of the 2p-electrons in chlorine increases the spin-orbit splitting by ϳ80 cm Ϫ1 , while in bromine we observe incremental increases of 130, 145, and 93 cm Ϫ1 , when adding the 3d, 3p, and 2p electrons to the set of explicitly correlated electrons, respectively. For fluorine and chlorine the final basis set limit, all-electrons correlated results match the experimentally observed spin-orbit splittings to within ϳ5 cm Ϫ1 , while for bromine the Breit-Pauli operator underestimates the splitting by about 100 cm Ϫ1. More extensive treatment of electron correlation results in only a slight lowering of the spin-orbit matrix elements. Thus, the discrepancy for bromine is proposed to arise from the nonrelativistic character of the underlying wave function.

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The accuracy of employing eective core polarization potentials (CPPs) to account for the eects of core-valence correlation on the spectroscopic constants and dissociation energies of the molecules B 2 , C 2 , N 2 , O 2 , F 2 , CO, CN, CH, HF, and C 2 H 2 has been investigated by comparison to accurate all-electron benchmark calculations. The results obtained from the calculations employing CPPs were surprisingly accurate in every case studied, reducing the errors in the calculated valence D e values from a maximum of nearly 2.5 kcal/mol to just 0.3 kcal/mol. The eects of enlarging the basis set and using higher-order valence electron correlation treatments were found to have only a small in¯uence on the core-valence correlation eect predicted by the CPPs. Thus, to accurately recover the eects of intershell correlation, eective core polarization potentials such as the ones used in the present work provide an attractive alternative to carrying out computationally demanding calculations where the core electrons are explicitly included in the correlation treatment.