Browsing by Author "Dr. Muhammad Ashfaq Ahmed"

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    A First-principles Study of Phonon Lattice Thermal Conductivity of Sulvanite Compounds
    (Library Information Services, COMSATS University Islamabad, Lahore Campus, 2023) Misbah Ullah Khan; CIIT/FA21-RPH-010/LHR; Dr. Muhammad Ashfaq Ahmed; LHR TP 8583
    Density functional theory is used to study sulvanite compound(VCu3S4) both the cubic and tetragonal phase. The lattice parameter in case of tetragonal phase is as following, 𝑎 = 𝑏 = 5.3096 while the ratio of 𝑐 ⁄𝑎 = 1.05 which shows that 𝑐 = 5.5750 under relax calculation. While in case of cubic 𝑎 = 𝑏 = 𝑐 == 5.4642. both phases are first optimized and found the minimum energy at these values of the lattice vectors. Both the phases are observed to have indirect band gap and the band gap is found to be 1.88eV for tetragonal phase and 1.01eV eV for cubic phase. Partial density of state and total density of state are also studied which provide further confirmation of the band gap and other electronic properties of the material. Boltztrap code is used to investigate the thermoelectric properties of both the phases of the material (cubic and tetragonal phase). We determined the ZT values, for cubic phase the highest ZT value achieved at CBM is 0.75 at 500K temperature and at VBM the highest value is 0.73 at 800K. while in case of tetragonal phase the highest ZT achieved at CBM is 0.85 at 1200K temperature and at VBM the highest ZT value is 0.8 at 1100K temperature. The values of ZT shows that the material is good for thermoelectric purposes. Also, the novelty of this manuscript is the study of the tetragonal phase of the material, which looks good regards to the ZT value.
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    Sulphide Based Quantum Dots For Energy Devices
    (Library Information Services, COMSATS University Islamabad, Lahore Campus, 2020) M. Talha Shahid; FA16-BPH-00; Dr. Muhammad Ashfaq Ahmed; LHR TP 5924
    Supercapacitors (also known as electrochemical capacitors or ultracapacitors) are a class of electrochemical energy storage devices with advantages including high power density, long cycle life, high dependability, short charging time, and low maintenance cost. The bottleneck of the modern electrochemical capacitors (ECs) in the market is their low energy density compared with that of commercial lithium-ion batteries (120–170 Wh kg−1). In general, ECs can be classified into two main categories based on their charge storage methods: