The accuracy of the pseudopotential approximation. I. An analysis of the spectroscopic constants for the electronic ground states of InCl and InCl3 using various three valence electron pseudopotentials for indium

Abstract

Spectroscopic constants for InCl and InCl₃ 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 InCl₃. The single‐electron adjusted energy‐consistent pseudopotential of Igel‐Mann et al. [Mol. Phys. 65, 1321 (1988)] 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=〈n‖P(R)‖n〉, 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, ‖0〉, the calculated property P₀ 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.