http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/275 2026-04-07T01:56:27Z 2026-04-07T01:56:27Z Hossain, Mohammad Alamgir http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/3583 2025-02-09T06:32:53Z 2025-02-09T00:00:00Z

Orbital Free Ab Initio Molecular Dynamics Simulation Study of Static and Dynamic Properties of Liquid Binary Alloys Hossain, Mohammad Alamgir Recently, ab initio molecular dynamics simulation has been an effective tool to study different physical properties of condensed matters. Simulation using the Kohn- Sham orbitals is much accurate in principle, but it demands very long computational time. As a consequence, it limits the number of particles (just few hundreds) in a periodic cell. This limitation may be largely overcome by employing the orbital free ab initio molecular dynamics (OF-AIMD) simulation method. This method is based on the Hohenberg-Khon version of the Density Functional Theory (DFT). Here the exchange and correlation functions are treated by the local density approximation (LDA). Specefically, in the present work we have studied some static and dynamic properties of NaK liquid metallic binary alloys. The static properties involve the static structure factors, isothermal compressibility, partial coordination number etc. The dynamic properties studied are dynamic structure factors, shear viscosity, diffusion coefficients, and velocity of sound. Static and dynamic properties calculated from the OF-AIMD simulation data are found to be good in agreement with the available experimental and other simulation data. This Dissertation is submitted to the Faculty of sciences, University of Dhaka as Fulfillment of the Requirement for the Degree of Doctor of Philosophy (Ph.D.) in Theoretical Physics.

2025-02-09T00:00:00Z Rana, Md. Masud http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/1804 2021-12-21T06:30:02Z 2021-12-21T00:00:00Z

Study of the Crystallization Kinetics of Amorphous Magnetic Materials Rana, Md. Masud Amorphous state of materials is a metastable state, which transforms into more stable crystalline phase while subjected to appropriate thermal treatment. Nanocrystallization of amorphous metallic magnetic ribbons by annealing above their crystallization temperature renewed enormous scientific and technological interest as a materials of state-of-the-art applications. In this research work we have focused on the study of understanding the crystallization behavior and magnetic properties of such nanocrystalline alloys with respect to annealing parameters, grain size and the crystalline volume fraction. Two series of amorphous ribbons of alloy compositions, (I) Fe73.5-xCrxNb3Cu1Si13.5B9 (x = 1, 5, 10, 12.5 and 17.5) and (II) Fe76.5-xNbxCu1Si13.5B9 (x = 1, 2, 3, 4, 5, 6 and 7) are cast by melt spinning technique and annealed at different temperatures based on thermal analysis data to prepare samples of varying nanocrystalline states. The magnetic, electrical and structural properties are investigated by VSM, Impedance Analyzer, XRD, FESEM and Mössbauer Spectrometer. The crystallization behaviors of as cast amorphous samples are studied by DSC technique. The volume fractions of amorphous and crystalline phases have been confirmed by the Mössbauer Spectrometry. Result obtained from detailed study show that crystallization kinetics of both the series of prepared samples are dependent on contents of refractory metals Cr and Nb substitution. The role of both Cr and Nb is to inhibit the process of crystallization and hinder grain growth and shift the crystallization temperature towards the higher temperature imparting enhancement of thermal stability of the amorphous alloys against crystallization. This unique behavior facilitates controlled nanocrystallization of the amorphous samples by annealing that finally give novel magnetic properties. Experimentally it is verified that Nb is more powerful in controlling the crystallization kinetics then Cr. It has been observed that amorphous alloys with Cr = 1, 5 and Nb = 3, 4 are suitable alloy compositions for better soft magnetic properties while annealed at Ta = 550oC and seems to be agree well with Herzer’s Random Anisotropy Model (RAM). This dissertation summited to the Department of Theoretical Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Theoretical Physics.

2021-12-21T00:00:00Z Molla, Mohammad Riazuddin http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/969 2019-11-03T04:23:52Z 2019-05-20T00:00:00Z

Study of the Bulk Properties of Liquid Transition Metals Molla, Mohammad Riazuddin Due to versatile applications of transition metals it is always interesting to study the properties of these metals and their alloys theoretically. The properties of transition metals largely depend on the electronic configuration of the outermost shell or nextto- outer most shell. We have studied some static and dynamic properties for liquid transition metals by using the orbital free ab initio molecular dynamics (OF-AIMD) simulation technique at thermodynamic states near their respective melting temperatures. The systems studied are the 3d (Cr, Mn, Fe, Co, Ni, Zn), 4d ( Pd, Cd) and 5d (Pt, Hg) liquid transition metals. Due to the availability of experimental data for static structure factor we have also performed simulation at several thermodynamic states for some systems, namely for liquid Fe (l-Fe), l-Zn, l-Hg, and l-Co. The OF-AIMD simulation technique is related to the density functional theory (DFT) of Hohenberg and Kohn. The exchange correlation energy is described by the local density approximation. To describe electron-ion interaction, we have used a model local pseudopotential proposed by Bhuiyan et al., which has proven to be the successful to generate the structural and dynamical properties of some liquid transition metals. The calculated results are presented here for a range of static structural magnitudes, such as static structure factor, isothermal compressibility, pair distribution function and coordination number. A comparison with the available X-ray and neutron diffraction data shows that the OF-AIMD method can provide a reasonable description of the static structure. As for the dynamic properties, results are reported for both single and collective dynamics. The calculated dynamic structure factors show side peaks which point to the existence of collective density excitations, from where the adiabatic sound velocities are calculated. Finally, we have performed calculation of some transport coefficients and obtained results are compared with the corresponding experimental data. Calculated results for static and dynamic properties are found to be good in agreement with available experimental data. We also have observed through the present work that a heavy computational demand of Kohn-Sham orbital representation of DFT used in AIMD can be partly overcomed by the OF-AIMD simulation method. This dissertation submitted for the partial fulfillment of the requirements for the Degree of Doctor of Philosophy in the subject of Theoretical Physics.

2019-05-20T00:00:00Z Abbas, Md. Fysol Ibna http://reposit.library.du.ac.bd:8080/xmlui/xmlui/handle/123456789/371 2019-10-06T09:03:00Z 2019-10-06T00:00:00Z

Thermodynamic and transport properties of aluminium (Al)-based liquid binary alloys Abbas, Md. Fysol Ibna In this thesis, the thermodynamic and transport properties of Aluminum (Al) based liquid binary alloys (Al1xXx, here X=Zn, In, Sn, Bi, Cu, and Au) are systematically theoretically investigated. The thermodynamic properties of liquid binary alloys which are named as the free energy (A), the energy of mixing ( A), the enthalpy of mixing ( H) and the entropy of mixing ( S) have been studied. Atomic transport properties (ATP) such as the coe cients of shear viscosity ( ), the di usion coe cients (D), and the friction coe cients ( ) are theoretically calculated for Al-based liquid binary systems. On the other hand, for electron transport properties, I have also studied the electrical resistivity ( ) and conductivity theoretically. The general microscopic theory (GMT) is employed to describe the inter-ionic and electron-ion interactions of the above metals. The inter-ionic interaction and a reference liquid are the fundamental components of this theory. For understanding the inter-ionic interactions in the high temperature liquid state, the Bretonnet-Silbert (BS) model has been used and extended it for simple metals (Al, In, Sn, Bi). This model treats sp and d bands separately within the well established pseudopotential mechanism. A liquid of hard spheres (HS) of two di erent e ective diameters and charges is used to describe the reference system. The LWCA thermodynamic perturbative method is used to calculate the e ective hard sphere diameter and the partial structure factor, Sij (q). For studying ATP, the distribution function method has been used which was proposed by Rice-Allnatt (RA) and is very convenient for numerical calculations due to its simple form. More importantly, the physical signi cances of each term in the theory are very transparent for understanding various transport mechanisms involved. Besides, studying the ETP for di erent liquid binary alloys, extended form of Faber and Ziman (1965) formula has been employed to calculate the electrical resistivity. Ziman's theory is based on the Nearly Free Electron (NFE) model and predicting reasonable values for resistivity of liquid metals, and this theory has been extended here for liquid binary systems. In addition, I have also studied the thermodynamic and transport properties such as the excess entropy, the shear viscosity and the di usion coe cient using the Universal Scaling Laws (USL) proposed by Dzugutov for single system namely for Al. Excess entropy is the main ingredient in the USL. Results for both thermodynamic and transport properties of Aluminum (Al) based liquid binary systems agree well with the available experimental data. This thesis submitted for the degree of Doctor of Philosophy in The University of Dhaka.

2019-10-06T00:00:00Z