Computation of Electronic Spectra of Molecules in Strong Magnetic Fields using Linear Response of Hartree-Fock Theory

Rahul, Raj K. (2022) Computation of Electronic Spectra of Molecules in Strong Magnetic Fields using Linear Response of Hartree-Fock Theory. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Rahul Raj K (17MS202)) 17MS202_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (7MB)

Abstract

External magnetic fields can have an e↵ect on the electronic structure of molecules when the field interaction strengths are comparable with Coulomb interactions. For small atoms/molecules, magnetic field strengths of around 235 kT or 1 au can alter the electronic spectra. In nature, white dwarfs and neutron stars have magnetic fields of this order. The observed electronic spectra available from white dwarf stars are strongly distorted by magnetic fields, and it is difficult to interpret them in connection with atomic and molecular structure. In this project, we compute the electronic spectra of molecules under a strong magnetic field using the random phase approximation (RPA), also known as the linear response of Hartree-Fock theory or time-dependent Hartree-Fock theory. Here our goal is not to accurately calculate the excitation energies but to understand the modification induced by the magnetic field compared to the zero-field case. The ground state is optimized in the presence of an external magnetic field, and the excited states are obtained via linear response. London atomic orbitals (LAOs) are employed to enforce gauge-origin invariance and accelerate basis set convergence. We also compute the spectral intensities in order to explore how the symmetric forbidden transitions become allowed in the presence of magnetic fields which lift this symmetry. We try to justify the changes in the electronic spectra at the level of orbital changes due to the magnetic field. 6

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