RT info:eu-repo/semantics/bachelorThesis
T1 Estudio mecano-cuántico del Nitruro de Galio desde primeros principios
A1 Lorenzo Domínguez, María
A2 Grado En Física
AB For the last few decades quantum-mechanical studies of materials have contributed togreat advances in materials science and its applications, facilitating the obtention of resultsin a less complex way than experimentally. In this report Galium Nitride has been studiedin order to understand its behavior when being affected by high pressures.To perform the ab initio simulation of the Gallium Nitride it is needed to explain thetheoretical background in which it is based. As it is in the quantum mechanical frame,the total energy Hamiltonian must be solved, but to do so, it is necessary to bring out someapproximations. The first one is the Born-Oppenheimer or adiabatic approximation, in whichthe problem is reduced to a system of electron in a frozen-in configuration of the nucleus. [1]After that, the density functional theory is considered, which stablishes that the system isformed by non-interacting electrons in an external potential and that the energy of the systemis a functional of the density of states. This theory was proposed by Kohn & Hohenberg,who also described the energy functional as a sum of two contributions: one related to theexternal potential and the other one related to a universal functional. The form of the lastone was given by Kohn & Shan. They established that the functional was composed of thekinetic energy of the electrons and the exchange-correlation energy. They also proposed a setof equations to be solved by self-consistent methods that can be used to obtain the densityof states and the external potential that solve the energy equation.By obtaining the total energy of the system, it is possible to obtain other variables andparameters of it, such as the pressure, the enthalpy, structural parameters, etc. The energiesand volumes obtained by the ab initio simulation can be adjusted to the Birch-Murnaghanequation of state. By doing that, the equilibrium constants can be obtained.In this work, the ab initio simulation was performed to study the evolution of the GaNat high pressures, where a transition phase can be observed. This transition takes placefrom a wurtzite phase to the rock salt, at 45 GPa, according to the calculations of this workcarried out with VASP (Vienna Ab initio Simulation Package). The wurtzite phase has twostructural parameters, c/a and u. At equilibrium, the obtained values were a0 = 3.179˚A andc0 = 5.179˚A, which are in accordance with the bibliography. The rock-salt structure onlyhas one parameter, a0 = 4.217˚A. The other equilibrium constants are collected in the tables2 and 3.It is also possible to calculate the electronical band structures for both phases, in whicha band gap of 1.63 eV was obtained for the wurtzite (at p=0) , and one of 1.21 eV for therock-salt at the transition pressure. The values are smaller than the experimental ones as theuse of GGA underestimates the energy gap.All these calculations were done using an energy cutoff of 600 eV and Rk = 24 for theconstruction of the k-points grid.
YR 2022
FD 2022
LK http://riull.ull.es/xmlui/handle/915/29109
UL http://riull.ull.es/xmlui/handle/915/29109
LA es
DS Repositorio institucional de la Universidad de La Laguna
RD 29-nov-2024