Quantum computer simulation of surface chemical reactions and vibration

Abstract

Many of today’s technologies for solar cells, catalysts and highly efficient lighting, come from the use of a conductive surface such as a metal or semiconductor, surface-dosed with other molecular species. These surface additives adhere to the substrate via adsorption, rather than being absorbed into the structure of the main material. Given the adsorbates are added at nanoscale dosages, the reactions take place at a quantum level and cannot be predicted by using conventional chemistry. Therefore, without consideration of the complex electronic, chemical and vibrational properties of the surface interactions between different molecular species, it has been hard to predict the outcomes of adding different adsorbates to substrates. Lin says: ‘Simulations of the quantum surface reactions between chemicals are vital, since they enable us to undertake high-throughput screening of different combinations of materials.’ According to Lin: ‘Vibrational spectroscopy is one of the most important tools for the determination of the surface species generated upon molecular adsorption.’ Techniques used include Raman spectroscopy and scanning tunnelling microscopy (STM). The latter device employs a fine probe, tipped with silver or other appropriate element through which a voltage is generated. Within a vacuum, the tip is moved within nanometres of the surface of the materials being studied, such that an electron from the tip is induced to tunnel across the space between tip and material. By scanning the probe across the material at a constant height, an atomic-scale image is produced of the surface materials. However, Lin says: ‘The images produced by standard STM are not easy to interpret.’ A better technique for probing the dynamic vibrational modes of molecules is to use STM with spectra produced by inelastic electron tunnelling spectroscopy (IETS). Work over the next five years will concentrate on narrowing that gap through accounting for weaker force van der Waal interactions and by refining the short time Fourier transformation calculations. Currently, Lin is focusing on palladium and silver substrates and nanoclusters, and evaluating their ability to break apart the atomic bonds within alcohol molecules, with a view to using this technique to produce hydrogen fuel for transport and other industrial end uses. Both team leaders look forward to their data and simulations being used by researchers all over the world to develop highly efficient solar cells, new OLEDs and effective catalysts for industrial processes. All these technologies will contribute greatly to powering our future in a carbon-neutral fashion.