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Excited State Forces in Semiconductor Crystals from the GW and Bethe-Salpeter Equation Methods

Vries, Alwin de (2024) Excited State Forces in Semiconductor Crystals from the GW and Bethe-Salpeter Equation Methods.

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Abstract:Research into the forces caused by photo-induced excitation of semiconductors is currently very computationally costly. This report aims to set a benchmark of forces in silicon to which results of future analytical methods can be compared. Silicon is studied using first-principles numerical modelling techniques, namely density functional theory as implemented in quantum espresso and the GW and Bethe-Salpeter Equation approach as implemented in the berkeleygw code. The lattice parameter of silicon was calculated to be 5.471 Å, which is in good agreement with experimental reference values. We then mapped out the excited-state energy landscape of silicon by calculating excited-state energies as a function of the interatomic distance of the two atoms in the primitive unit cell of fcc silicon. In these calculations, we observed exciton energies far above experimental values and no minimum energy was found. We therefore used a supercell approach, which allows us to calculate the energy of the indirect exciton. We found that even after relaxing the lattice parameter in the first excited state to 5.45 Å, there were still forces on the atoms, implying that some reconfiguration of the crystal also occurs during excitation. Keywords: excited state forces; density functional theory; GW and Bethe-Salpeter equation methods
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:31 mathematics, 33 physics, 51 materials science
Programme:Applied Physics BSc (56962)
Link to this item:https://purl.utwente.nl/essays/102090
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