University of Twente Student Theses


Excited-state geometries of small molecules from the GW+Bethe-Salpeter Equation approach

Hilt, M.J.G. (2023) Excited-state geometries of small molecules from the GW+Bethe-Salpeter Equation approach.

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Abstract:In this thesis the GW + Bethe-Salpeter equation (GW + BSE) approach is used to calculate the excited-state geometry of carbon monoxide and thioformaldehyde. The GW method is a many-body perturbation theory which in combination with BSE is able to provide accurate neutral excitation energies in a wide range of systems from molecules to extended solids. Using these neutral excitation energies in combination with ground-state energies obtained using density functional theory allows for the calculation of excited-state energies. Calculating these excited-state geometries with the GW + BSE approach is of importance because essentially all GW + BSE calculations that have been performed to date assume that the excited-state geometry is equal to the ground-state geometry. Other methods have been used to calculate excited-state geometries such as the wavefunction-based equation of motion coupled cluster with single and double excitations (EOM-CCSD) and third order coupled cluster (CC3) methods but these scale with O(N 6) and O(N 7) respectively. The GW + BSE approach scales better with O(N 4) where N denotes the amount of electrons in the system. A systematic benchmark is performed to evaluate how well excited-state geometries from GW+BSE approach agree with reference results from CC3 and EOM-CCSD.
Item Type:Essay (Bachelor)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:31 mathematics
Programme:Applied Mathematics BSc (56965)
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