Recent News

  • Oct 2021: Yann Damour has (re)joined the group as a PhD student. Welcome back Yann!
  • Aug 2021: Antoine’s paper on variational pair CCD for ground and excited states has been accepted in JCP!
  • Jun 2021: Fabris' paper on pair CCD for excited states has been accepted in JCTC!
  • Jun 2021: Raul Quintero-Monsebaiz has joined the group as a postdoctoral fellow. Welcome Raul!
  • Mar 2021: Enzo’s first paper on spin-flip BSE has been accepted in JCTC!
  • Feb 2021: Our paper on perturbation theory in the complex plane has been accpeted in JPCM!
  • Dec 2020: The QUEST website is officially online and the corresponding publication submitted!
  • Oct 2020: Fabris Kossoski has joined the group as a postdoctoral fellow. Welcome Fabris!
  • Oct 2020: A new PhD student (Enzo Monino) has joined the group. Welcome Enzo!
  • Jun 2020: The ERC PTEROSOR project has officialy started!

The PTEROSOR project

Processes related to electronically excited states are central in chemistry, physics, and biology, playing a key role in ubiquitous processes such as photochemistry, catalysis, and solar cell technology. However, defining an effective method that reliably provides accurate excited-state energies remains a major challenge in theoretical chemistry. In PTEROSOR, we aim at developing a totally novel approach to obtain excited-state energies and wave functions in molecular systems thanks to the properties of non-Hermitian Hamiltonians. Our key idea is to perform an analytic continuation of conventional computational chemistry methods. Indeed, through the complex plane, ground and excited states can be naturally connected. In a non-Hermitian complex picture, the energy levels are sheets of a more complicated topological manifold called Riemann surface and they are smooth and continuous analytic continuation of one another. PTEROSOR’s main goal is to develop a new theoretical approach allowing to connect, through the complex plane, electronic states. Instead of Hermitian Hamiltonians, we propose to use a more general class of Hamiltonians which have the property of being PT-symmetric, i.e., invariant with respect to combined parity reflection P and time reversal T. This weaker condition ensures a real energy spectrum in unbroken PT-symmetric regions. PT-symmetric Hamiltonians can be seen as analytic continuation of conventional Hermitian Hamiltonians. Using PT-symmetric quantum theory, an Hermitian Hamiltonian can be analytically continued into the complex plane, becoming non-Hermitian in the process and exposing the fundamental topology of eigenstates. Our gateway between ground and excited states are provided by exceptional points which lie at the boundary between broken and unbroken PT-symmetric regions.

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 863481).