# Category Archives: Theoretical physics

## Surface-Enhanced Molecular Electron Energy Loss Spectroscopy

Chemists have a range of different spectroscopic techniques to study organic molecules. All of these techniques are based on spectra generated by a range of electronic transitions and vibrations, key excitations in matter, the study of which provides information about […]

## HOTI bismuth

The properties of bismuth have long defied classification, placing it in a category of its own. Now, as if it was not enough, it turns out its electronic structure has higher-order topology. This has been shown by an international team […]

## The microscopic mechanism behind the vibrational relaxation of adsorbates on metal surfaces

Most of the theories describing dynamical processes at surfaces rely on the validity of the adiabatic Born-Oppenheimer approximation. What does this mean? We have already seen that adsorption commonly is understood as the reversible binding of molecules and atoms […]

## Has theoretical physics become a sleeping beauty?

The progress that physics experienced during the 20th century was probably one of the greatest and most everlasting successes of the humankind. Discovering the hidden and minute composition of matter and energy, as well as realising that the […]

## Beyond the point-dipole approximation

The wave nature of light expresses itself in the propagation all over space, showing an intrinsic limitation to be localized beyond the so-called diffraction limit which is of the order of half the wavelength of the photons propagating. However when […]

## Remarks on Moduli Spaces and String Theory

The concept of moduli space is of utmost relevance in theoretical physics and mathematics, especially in geometry, topology and string theory. A moduli space is, roughly speaking, a space that classifies a given class of objects modulo an equivalence […]

## How to extract the interacting spectral function from a ground state DFT calculation

The electronic wave function of an n-electron molecule depends on 3n spatial and n spin coordinates. In a sense, the wave function of a many-electron molecule contains more information than is needed and is lacking in direct physical significance. This […]

## Higher-order topological insulators

Topological insulators are materials with special universal properties, which are protected against perturbations. Such properties are theoretically described by topology, a branch of mathematics concerned with the properties of geometrical objects that are unchanged by continuous deformations. Concretely, topological insulators […]

## The size of atoms, uncertainty and relativity

You may have read somewhere that atoms are actually made up mostly of empty space. The usual description goes more or less as follows. At the centre of each atom there is a very tiny nucleus, which carries all of […]

## Family unification (2): The SO(18) spinor strikes back

In the previous post, Family unification 1, we reviewed the historical development of Grand Unified Theories (GUT) of force and matter, i.e. Comprehensive Unification. We saw how the SO(18) spinor, 256, is able to accomodate the Standard Model […]