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«Vibrational spectroscopy beyond the harmonic approximation with the Polarizable Embedding model»

 

Popular scientific abstract:

In order to efficiently and accurately calculate vibrational properties for solvated systems, a theoretical framework for combining response theory with the Polarizable Embedding model (PE) has been derived and implemented, and is presented in this thesis.

An open-ended recursive formalism is utilized through the implementation in OpenRSP, allowing energy-derivatives to be calculated analytically up to arbitrary order.
In this way, errors associated with numerical differentiation are avoided, and calculations of properties of higher order can be performed without the need for additional implementation.
The PE model is a focused embedding model, and includes solvent effects through both static and instantaneous interaction energies between a central molecular region and a surrounding environment.
The central region is modelled using quantum-mechanical methods (and therefore is commonly referred to as the QM region), whereas the environment is treated through classical multipoles and polarizabilities.
The multipoles and polarizabilities are placed on so-called sites, typically located on the atoms in the environment.
This retains a discrete atomistic model while still considerably reducing the overall computational cost compared to a full quantum mechanical description.
The method allows the user to automatically calculate the multipoles and polarizabilities, thereby avoiding any need for using predetermined parameters.
In addition to its efficiency, the PE method is thus both accurate and flexible.
In this thesis, a new combination of the PE method with the open-ended response framework is presented, in addition to the implementation done in order to calculate various vibrational frequencies and intensities from the calculated energy derivatives.

The theoretical background for derivatives of the PE energy is outlined, and software for the calculation of these has been developed through a combination of the LSDalton, OpenRSP and FraME programs.
A new software package, SpectroscPy, has been developed in order to calculate spectroscopic frequencies and intensities, for either vacuous or solvated systems.
The current version of the program allows the user to produce IR, Raman and hyper-Raman spectra.
The implementation can be extended to better model repulsion interactions between the QM region and the environment through the Polarizable Density Embedding method.
Newer versions of the implementation should also contain the functionality necessary to perform calculations on biomolecules, as it for the moment only allows systems where no covalent bonds need to be cut in the partition of the QM region from the environment, and/or between the environmental fragments.
Once magnetic derivatives are available through OpenRSP, implementation of vibrational-rotational spectroscopic properties is also a route that should be investigated.

The thesis is published in Munin and is available at:  https://hdl.handle.net/10037/20569

 

Supervisors:

• Professor Kenneth Ruud, Department of Chemistry, UiT (main supervisor)
• Researcher Magnus Ringholm, Department of Chemistry, UiT
• Senior Lecturer Maarten Beerepoot, Department of Chemistry, UiT
• Researcher Jógvan Magnus Olsen, Department of Chemistry, UiT

 

Evaluation committee:

• Dr. Filippo Lipparini, Department of Chemistry and Industrial Chemistry, Università di Pisa, Italy (1. Opponent)
• Professor Sandra Luber, Department of Chemistry, Universität Zürich, Switzerland (2. Opponent)
• Professor Luca Frediani, Department of Chemistry, UiT (internal member og leader of the committee)

Reserve member: Professor Hanna-Kirsti Schrøder Leiros, Department of Chemistry, UiT

Both opponents will participate remotely to the defence.

 

Leader of the public defense:
The leader of the public defense is Professor Camilla Brekke , Vice Dean Research, Faculty of Science and Technology, UiT.

 

Opposition ex auditorio:
If you have any questions for the candidate during the public defence, please send an e-mail to the leader of the public defence. They will announce the questions during the defence.

 

Trial lecture:

The trial lecture is held Tuesday February 23rd at 10:15 AM in the same auditorium.

Title of the trial lecture: «Intermolecular interactions: computational modeling and benchmarking»

 

Streaming:

The defense and trial lecture will be streamed via Mediasite: 

https://mediasite.uit.no/Mediasite/Catalog/Full/4b2db54962fc422e8f531fadf5215d1421

 

Audience:

UiT follows the national guidelines regarding infection control. A maximum of 20 people are allowed in the auditorium during the defence, as long as everybody keeps a distance of 1 meter at all times.