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Investigation of Thermodynamic and Dynamic Properties of Some Solids and Fluids with Nano Dimensions Using Molecular Dynamics Simulation

Akbarzadeh, Hamed | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42083 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Parsafar, Gholam Abbas
  7. Abstract:
  8. The physical characteristics of Pt nanoclusters with different sizes (256-8788 atoms) have been investigated via molecular dynamics simulations. The Pt-Pt radial distribution function, internal energy, heat capacity, enthalpy, entropy of the nanoclusters are calculated at some temperatures. The melting point predicted by the various properties is consistent with each other and shows that the melting temperature increases with the particle size. We have calculated the Gibbs free energy for the Pt bulk and also for its nanoparticle. We have used the thermodynamic integration method to obtain the Gibbs free energy. The total Gibbs free energy is taken as the sum of its central bulk and its surface free energy. We have calculated the free energy of a platinum nanoparticle as a function of temperature. We present an approach for constant-pressure molecular dynamics simulations. A molecular dynamics (MD) simulation for Ni nanoclusters is used to calculate their pressure–volume–temperature data for the temperature range 200 K≤T≤400 K. We have found that some EoSs are valid for both bulk Ni and Ni nanoclusters, but with different values of the parameters, which depend on the cluster size and temperature. An increase in bulk modulus with decrease of cluster size can be observed. Also, we have investigated the size dependence of a nano-cavity properties produced in a Xe fluid. We have created a nano-cavity of different sizes at 170 and 200 K (cavities diameters are within 1- 10 nm). Liquid pressure, vapor pressure and surface tension of the nano-cavity for some given values of diameter are calculated. Within 1- 10 nm cavity diameter, we have observed two opposite behavior for the dependency of surface tension on the cavity diameter: for the range of 1-5 nm, it increases with the diameter, while, for the range of 5- 10 nm remains constant. Finally, The interaction potential energy and heat of sublimation of nanoparticles of HMX crystal polymorphs are studied. Molecular dynamics simulations of nanoparticles with 10- 100 molecules of HMX are carried out at 300 K. The intermolecular, intramolecular and total interaction energies per mole for the nanoparticles are calculated. For the all sizes, β – HMX is found to be the most stable phase, due to having the least total interaction energy. An increase in the sublimation enthalpy with the size of the nanoparticle can be seen.
  9. Keywords:
  10. Nano-Cluster ; Molecular Dynamic Simulation ; Thermodynamic Properties ; Size Effect

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