Computational screening for effective Ge1-xSix nanowire photocatalyst.

We perform a comprehensive mapping of GeSi nanowire (NW) electronic band characteristics versus the alloy composition and the diameter (up to 3 nm) using hybrid density functional theory (DFT) calculations, the cluster expansion method and Monte Carlo simulations. We reveal that stable alloy GeSi NW configurations across compositions tend to exhibit asymmetric core-shell structures, which enhance spatial separation of the band edges, making them more effective for electron-hole charge separation as compared to conventional symmetric core-shell structures. More importantly, from the composition-size map of the NW band edges, we show that GeSi NWs with diameters below 3 nm are thermodynamically capable of photocatalysing water-splitting reactions (alkaline conditions) and CO2 reduction. In particular, NWs with diameters of 2 and 3 nm possess desirable properties for efficient photo-conversion; their bandgaps (1.4 to 2.0 eV) match well with the solar spectrum.