Sidebar
Does chemistry need more physics ?
The building blocks of chemistry are organized in the periodic table, which requires quantum mechanics for its understanding. In the 1980s it was realized that in order to correctly describe the heavy elements in the lower part of the periodic table, the special theory of relativity had to be invoked. The HAMP-vQED projet will investigate the possible role of quantum electrodynamics (QED) in chemistry. It will provide a protocol for highly accurate calculations of molecular properties, with particular attention to properties that probe the electron density in the close vicinity of atomic nuclei, where the QED-effects associated with the Lamb shift are created. The HAMP-vQED adheres to the general framework of quantum chemistry by seeking a variational (non-perturbative) approach using local (Gaussian) basis functions.
Is the vacuum really empty ?
An ideal situation for accurate calculations is a molecule alone in space at 0K. However, is the vacuum really empty ? It has been shown that placing a molecule in an otherwise empty cavity will change its reactivity [1]. This is explained by the coupling of the molecule to the zero-point vibrations of the quantized electromagnetic field.
In the HAMP-vQED we are particularly interested in the effects leading to the Lamb shift, a splitting between the 2S1/2 and 2P1/2-levels of one-electron atoms, not predicted by the Dirac equation, but observed for the first time in 1947 by Lamb and Retherford.
- Vacuum polarization: A charge in space is surrounded by virtual electron-positron pairs. This will contribute to the observed charge.
- Electron self-energy: A charge drags along its electromagnetic field. This will contribute to the observed mass.
The splitting is a mere 4 meV, but for hydrogen-like uranium the splitting has grown to an impressive 468 eV. It is therefore legitimate to ask if QED-effects could play a role in the chemistry of heavy elements.
Project objectives
- Set new standards for correlated relativistic molecular calculations, with particular focus on properties probing nuclear regions
- Develop a variational approach to QED rather than the usual perturbative one (QED without diagrams)
The most challenging part of the project is to devise ways of handling the divergences of QED using the computational framework of quantum chemistry.
References
[1]. J.A. Hutchison, T. Schwartz, C. Genet, E. Devaux, and T. W. Ebbesen, “Modifying Chemical Landscapes by Coupling to Vacuum Fields”, Angewandte Chemie International Edition 51, 1592–1596 (2012).
