Relativistic Gaussian basis set calculations on one-electron ions with a nucleus of finite extent

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The disadvantages of using Gaussian functions (GTOs) in SCF electronic structure calculations are well known. The difficulties associated with Gaussians are likely to be more severe in relativistic Dirac-Fock calculations. Relativistic effects are important for core electrons, whereas GTOs give a poor description near the nucleus. By changing the boundary condition on the wavefunction at the origin, it may be possible to remove some of the difficulty. In calculations on O 7+ and Hg 79+ we explore the effect of replacing the point model of the atomic nucleus by a nucleus of finite size. We find that smaller basis expansions are required for the heavier nucleus in the finite-nucleus model.