Browsing by Author "MUHAMMAD FAIZAN KHAN"

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    Vibrational and thermodynamical properties of SmX (X = S, Se, and Te) chalcogenides
    (UMT, Lahore, 2019) MUHAMMAD FAIZAN KHAN
    In the present work, structural, vibrational and thermodynamic properties of SmX (X = S, Se, Te) compounds are computed and compared with the available literature. The structural calculations are carried out using Density functional Theory (DFT) with Generalized Gradient Approximation (GGA) as an exchange-correlation potential. The vibrational properties are calculated using Density Functional Perturbation Theory (DFPT) with Martin-Troullier as a norm conserving pseudopotential. The thermodynamic properties are investigated using quasi-harmonic Debye model for temperature range 0 – 1000K in Gibbs-code with optimized data obtained from Wien2k-cde. Phonon dispersion curves for SmS, SmSe, and SmTe indicate that there is no imaginary phonon frequencies in the entire Brillouin zone, which proves the dynamical stability of these materials. SmS has the largest and SmTe has the smallest phonon band gap which somehow suggests the polar property of SmX materials. The phonon gap or vibrational gap for SmS, SmSe and SmTe are about 228.067 cm-1, 156.805 cm-1 and 128.012 cm-1, respectively. For all compounds, the three acoustic modes near the gamma point have a linear behavior. Cv is a function of T¬¬3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected. The variation of specific heat with temperature has been discussed in detail in the thesis.