Properties of High-Performance Capacitor Materials and Nanoscale Electronic Devices

Recent advances in theoretical methods combined with the advent of massively parallel supercomputers allow one to reliably simulate the properties of complex materials and device structures from first principles. We describe applications in two general areas: i) novel polymer composites for ultra-high-density capacitors, necessary for pulsed-power applications, such as electric rail guns, power conditioning, and dense electronic circuitry, and ii) electronic properties in nanoelectronic devices, such as graphene nanoribbons and C₆₀-based devices. For capacitor materials, polyvinylidene fluoride (PVDF) with a small concentration of chlorotrifluoroethylene (CTFE) has been observed to store very high energy as compared to currently used polymers. We have recently suggested that the ultra-high energy storage is due to an electric-field-induced phase transition from the non-polar α to the polar β-PVDF. We have now extended our investigations to multi-component polymers and also to the initial stages of kinetics. Turning to nanoelectronic materials, we show that devices based on two C₆₀ molecules can display negative differential resistance at low voltages. We also explore the electronic structure and spin polarization of nitrogen-doped carbon nanoribbons, which are candidate materials for ultra-high-speed nanodevices. We find enhanced N segregation in zigzag nanoribbons, due to interplay between impurity states in the valence bands and the edge states. Spin distribution is significantly affected, even at edges that are quite far from the dopant. We also find that the three armchair nanoribbons (ARs) families, defined by mod (n, 3), behave differently in doping.