Are LCAO-MO Models Useful Estimators for Electric Field Gradients in Simple Molecules?

In this tutorial paper we compare the ab-initio calculations of electronic charge densities and related electric field gradients in simple molecules like H₂ as well as the triangular H₃ with variable bond distance and bond angle using the Amsterdam Density Functional (ADF) code with calculations based on a simple linear combination of hydrogen 1s-orbitals. In order to gain more insight into ADF – or other ab-initio – calculations it is rather useful to vary structural parameters. In addition to geometry optimisations we propose to vary bond distances and bond angles over extended ranges in order to arrive at a better interpretation of the results.