Sampling all possible material and environmental combinations is beyond our reach experimentally, but it is an ideal job for theory and simulation. Using analytical models we can rapidly and systematically sample this parameter-space to identify new control parameters and formation mechanisms.

In our study, thermodynamic modeling and first-principle computer simulations have been combined to explore the links between the size, shape, axial orientation and aspect ratio of the pyrite form of FeS2, and (abiotic) environmental parameters such as temperature, surface hydration and the abundance of chemical precursors present during formation. In particular, the adsorption of water and variations in the concentration of iron and sulphur are common to hydrothermal synthesis and biomineralization (and the degradation of iron sulphides in marine systems), and are assumed to be influential in the formation of particular shapes.

The results reveal that there is a close competition between pyrite nanorods with the principle axis oriented in the ±[001] or ±[011] directions. In general, ±[011] oriented nanorods with a hexagonal cross-section are favoured under ambient conditions, irrespective of sulphur concentration or hydration, but more than ~115 °C (in water) square ±[001] nanorods become thermodynamically favourable. These results suggest that water may well be a decisive factor in moderating basic morphological features, such as axial orientation, but that variations in sulphur concentration are less significant than previously thought.

The researchers presented their work in Nanotechnology.