Spin–orbit effects in the bismuth atom and dimer: tight-binding and density functional theory comparison

We present a simple tight-binding model for the bismuth atom and dimer whose main feature is the inclusion of the spin–orbit coupling in such a way that it allows the study of several electronic properties as a function of the spin–orbit coupling strength. Density functional theory calculations (norm-conserving and full-potential linearized augmented plane wave) are used to obtain the tight-binding parameters and to check the accuracy of the model. The model is then used to show in a straightforward way that, in the case of the bismuth dimer, the inclusion of the spin–orbit coupling produces a set of molecular orbitals that are a mixture of bonding and non-bonding non-relativistic molecular orbitals, thus weakening the molecular bond. (paper)