Skip to main content
KBS_Icon_questionmark link-ico


Personal webpage

Dr Cedric Weber at the Thomas Young Centre


Dr. Cedric Weber undertook his undergraduate studies at the Swiss Institute of Technology where he also gained a Masters and Ph.D. in Physics. In 2007 he became a Research Associate at Rutgers University in the USA and then moved to the UK in 2011 where he was a Research Associate at the Cavendish Laboratory in Cambridge. In 2012 he moved to his current position of lecturer at King’s College London.


Take a deep breath, you just created a quantum entangled state! 

Metalloporphyrin systems, organic compounds which contain a metal ion such as heme, the pigment within red blood cells, play a central role in biochemistry. 
The ability of such molecules to reversibly bind small ligands is vital for life, particularly in heme, which can bind diatomic molecules such as O$_2$ and CO. Crucially, heme is the primary transport molecule in human respiration. 

Although studied extensively, heme remains a mystery for physicist. Indeed, electronic structure calculations carried out early in the last decades found that whereas O$_2$ binds reversibly, the toxic ligand CO binds irreversibly! 

In a recent work appeared in Physical Review Letters, we used state of the art DFT+DMFT quantum calculations (combination of Linear-Scaling Density Functional Theory and Dynamical Mean-Field Theory, using the ONETEP package) to study the binding of oxygen and carbon monoxide to the heme molecule. 

We found that quantum effects are important to describe this simple molecule. This is due to the effect of electronic correlations (N-body problem), called "strong correlations", and are induced by the presence of the iron atom, a transition metal ion. 

The quantum many-body ground-state of heme is indeed a quantum superposition of different quantum states (it is entangled), and in particular the charge of the iron atom was found to be "fluctuating" (valence fluctuation). 
We also found that the Hund's rule, so far neglected to describe this simple molecule, plays a central role in reorganizing the electronic state of this molecule: a 3d orbital-selection process occurs beyond a critical value of the Hund's exchange coupling parameter J, by which out-of-plane orbital hybridization is enhanced and the difference of ligand binding affinities is strongly reduced (Picture below). 

This work offers a very detailed picture of the microscopic mechanisms of diatomic ligand binding to heme, and is among the first applications of DFT+DFMT to molecules, including total-energies, spectral properties in very good agreement with experiment, and transient magnetic response calculations.