Missions

Exploration of complex potential energy surfaces of molecular clusters
and simulation of low energy electrons dynamics following ionization

Irradiation of condensed matter by high energy, ionizing, particles (eXtreme UV, X, photons or fast charges particles) produces copious amounts of low energy electrons (LEE- few eV to a few tens of eV). In medicine and biology, the showers of LEE produced by irradiation are thought to be responsible for major deleterious lesions on DNA. In other contexts, namely astro- and exo-chemistry, the precise role of LEE generated in the interstellar space, on Jovian planet's moons atmospheres or on planet's ionospheres, expected to be major, is currently debated. Clusters/nanoparticles are ideal models to understand the size-evolution of structural/dynamical and electronic properties towards those of organized condensed matter.
The ANR BIRD project (BIrth, Relaxation and Diffusion of Low Energy Electrons in Condensed Phase) gathers complementary theoretical research groups with expertise in Density Functional Theory modelling of nanosystems, and experimental teams specialist of time-resolved photoelectron emission and manipulation of clusters and nanoparticles. The postdoctoral fellow will be hired by the theoretical team Molecules-Agregates-Dynamics of the Laboratoire de Chimie et Physique Quantiques of Toulouse. The general goal is to understand the structural and dynamical properties of molecules deposited on an inert atomic or molecular cluster including a few tens to a few hundreds of monomers (Argon, CO2, water or amonia).

Activities

(i)The first task will be a structural investigation to determine the favoured deposition sites and the induced inert cluster deformation, by means of global energy minimization algorithms on complex potential energy surface. In the past decade, our team has implemented and used several tools to deal with atomic and molecular clusters in the context of the Density Functional based Tight Binding method [1] (an approximated DFT scheme much faster than DFT). These schemes have been successfully used to determine the lowest energy structures for argon and water clusters or hydrocarbons trapped in these clusters [2]. The developments in the DFTB deMonNano code now allow for various global exploration schemes to be mobilized, ranging from simple Molecular Dynamics or Monte Carlo schemes to more sophisticated Basin Hopping and Parallel Tempering [3], threshold algorithm [4], and their coupling with local optimization schemes.

(ii) The second task will be to examine the dynamical behaviour of those weakly bound systems at the experimental temperature conditions via Molecular Dynamics.

(iii) In complement to those ground state studies, an exploratory part of the postdoctoral research will be to address non-adiabatic dynamics for electrons emitted after ionization of the deposited molecule. This will be feasible using a new orbital-Free DFT scheme [5] for the electronic dynamical evolution, conducted keeping fixed nuclei. The coupling of the electron dynamics with the nuclei motion could also be investigated using current non-adiabatic mean-field dynamics developments of DFTB.

1-Spiegelman F, Tarrat N, Cuny J, Dontot L, Posenitskiy E, Martí C, Simon A, Rapacioli M (2020). Adv Phys X 5:1710252. https://doi.org/10.1080/23746149.2019.1710252
2-Leboucher H, Simon A, Rapacioli M (2023). J Chem Phys 158:114308. https://doi.org/10.1063/5.0139482
3-Dontot L, Spiegelman F, Rapacioli M (2019). J Phys Chem A 123:9531–9543. https://doi.org/10.1021/acs.jpca.9b07007
4-Rapacioli M, Christian Schön J, Tarrat N (2021). Theor. Chem. Acc. 140:85. https://doi.org/10.1007/s00214-021-02748-7
5-White AJ, Certik O, Ding YH, Hu SX, Collins LA (2018). Phys Rev B 98:144302. https://doi.org/10.1103/PhysRevB.98.144302

Skills

The candidate should have a phd in theoretical physics and/or theoretical chemistry. The candidate will gain knowledge semi-empirical tight binding method and global exploration methods. A motivation for programming would be appreciated for the third part of the work.

Work Context

The post doctoral fellow will be hosted in the Laboratoire de Chimie et Physique Quantique and co-supervised by Mathias Rapacioli, Aude Simon and Fernand Spiegelman in collaboration with the two other teams of the ANR project, i.e. Aurélien de la Lande (Orsay, LCP) - Lionel Poisson (Orsay, ISMO)

Constraints and risks

No specific risk and constraints are associated to this project

Additional Information

The contract can be renewed for 8 months
Contract start date is flexible between November 2024 and February 2025.

Applications must include:

- a cover letter (please explain your motivation for joining the project, your future plans, your skills and what you will bring to the team - 1 pages maximum),

- a CV including a list of publications (with your contribution to the main publications), and the contact details of two referees.