We are deeply sad to report the recent passing of François Ducastelle who died on 2 July 2021.

François Ducastelle spent his entire career at ONERA. He was an internationally renowned physicist whose work on statistical physics and order-disorder transitions in alloys and more recently on the growth and spectroscopic properties of nano-objects (nanotubes, 2D materials) is widely recognized.

In the field of electronic structure of materials, many of François Ducastelle’s works are pioneering.  This includes the modelling of the excitation spectra of transition metals by a perturbation method on the Hubbard model. We can further mention the derivation of an effective Ising model, describing the thermodynamic and kinetic properties of alloys and metallic compounds, by the so-called generalized perturbation method (GPM) on the disordered state described in a Tight-Binding formalism and the Coherent Potential Approximation (CPA). Let us also cite his pioneering work on the method of moments, which is at the base of the N-body interatomic potentials and of order-N electronic structure methods used in the modern numerical simulations, or his elegant mathematical solution of the previously unsolved problem of calculating the electronic density of states in the form of a continued fraction for compounds or semiconductors presenting large band gaps. More recently, he developed Wannier Tight-Binding models to describe the excitonic properties of 2D materials.

He is the author of a book entitled “Order and Phase Stability in Alloys” on the theory of alloys, all fields considered together (electronic structure, statistical mechanics, …), which is a reference for all researchers involved in the area.

A strong feature of his research work comes under the double sign of his concern to extract from the electronic structure the essential ingredients driving the macroscopic properties accessible to experiments, and of its inclination for a mathematical physics based on elegant analytical developments.

Always active and involved in many projects, François Ducastelle maintained a collective research dynamic and numerous interactions with the international scientific community.  He also interacted with young researchers on a daily basis in a very humble way and with a great deal of humour.

We are deeply affected by his sudden death. He will remain in our memories and will continue to inspire us.

Guy Tréglia, Cyrille Barreteau and LEM (ONERA-CNRS)