Browsing by Author "Anwar-ul-Haq, Muhammad"
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Item Open Access Theoretical study of germanium nanoclusters: significance of surface passivation(Springer, 2022-03-07) Niaz, Shanawer; Gülseren, Oǧuz; Hussain, Safdar; Anwar-ul-Haq, Muhammad; Badar, Manzoor Ahmad; Khan, Muhammad AslamBy employing PBE and B3LYP, we report a density functional theory (DFT) and TDDFT investigation of X-terminated Ge nanoclusters (where X = bromine (Br), chlorine (Cl), fluorine (F), hydrogen (H), Amino (NH2) and hydroxyl (OH)). This research reveals that surface conditions considerably change the cohesive, structural, optical, and electronic properties of germanium nanoclusters, which plays a key role in the development of nano-devices, for instance, FETs, sensors, etc. We demonstrate that full coverage of nanocluster’s surface with the above-mentioned passivants/functional groups can reduce the HOMO–LUMO gap (and optical gap), for example, up to 1 eV of [110] Ge nanoclusters of 1.5 nm diameter. The following order of magnitude of the electronic gap is observed: H > NH2 > F > Cl > OH or Br. Partial density of states and graphical representation of HOMO and LUMO show that the Br and OH groups significantly lower gap energies, which is confirmed while observing the clear dominance of Br and OH near the HOMO compared with the Ge atoms. Moreover, in addition to the electronic/optical gap, the binding/cohesive energy of OH and Halide-terminated Ge nanoclusters exhibit greater stability compared with other passivants/functional groups.Item Open Access Theoretical study of hydrogen adsorption in Ti-decorated capped carbon nanotube(Taylor and Francis Ltd., 2017) Niaz, Shanawer; Abbasian, Hamed; Badar, Manzoor Ahmad; Anwar-ul-Haq, Muhammad; Karayel, ArzuWe present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses fromadsorption energy profile, highest occupied molecular orbital–lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques.