Applications are invited for a Postdoctoral Research Associate at Toulouse University (GET laboratory), working with Dr Merlin Méheut and Dr Magali Benoît (CEMES, Toulouse), in the framework of an ANR “Young Researcher” project. We are looking for talented and highly motivated candidates to realize molecular dynamics calculations (both empirical and ab initio) for Environmental Sciences. The Associate will collaborate with experimental scientists at GET (Coll G Saldi, J Schott) and LHyGeS, Strasbourg (Coll A.D Schmitt), and with chemical theoricists at ENS, Paris  (coll R. Vuilleumier), NYU (M. Tuckerman) and CMC, Strasbourg (R. Schurhammer). Candidates motivated by multidisciplinary research and application of atomistic simulation to complex natural systems will be appreciated.

To apply for this position, please connect to the following link : https://bit.ly/3oo5NyI

Scientific context
Isotopic compositions of natural phases constitute a tool of primary importance to assess geological history. Recent progresses in mass spectrometry and analytical chemistry have enabled the detection of isotopic variations of a host of elements (e.g. Fe, Mg, Ca, Li, Zn), opening the path to numerous applications. In particular, Ca isotopes have shown their potential for medical applications (early diagnosis of decalcification), to assess mechanisms occuring at the soil-plant interface, or to assess the Ca cycle in the environment.

To take the full extent of these new measurements, it is necessary to precisely constrain the isotopic effect associated with elementary processes occuring at the atomic level. In this perspective, the fractionation of isotopes reached at thermodynamical equilibrium (called equilibrium fractionation) between two phases (between one mineral and a dissolved species, or between two dissolved species) is of particular interest.

It is possible to estimate isotopic fractionation based on atomistic modeling by estimating the thermo-kinetic properties of atoms in a given bonding environment. For solids, these properties are generally estimated based on the harmonic approximation, starting from the vibrational frequencies of the mineral (e.g. Méheut and Schauble 2014). For liquids, we have developed an approach based on path integral molecular dynamics (PIMD, Dupuis et al 2017). This approach, which was applied to Li isotopes, is computationally very expensive, and that is why it has been limited so far to the use of empirical potentials to describe atomic interactions.

Our primary goal is to set an affordable numerical scheme to compute equilibrium fractionation properties of any material, in particular dissolved species, based on path integral molecular dynamics methods, but with atomic bonding described by ab initio electronic structure computations (instead of empirical potentials), so as to render its application to virtually any case. This approach will be first tested on the Ca²⁺-H2O system for which experimental data exist.

Description of the position:
The work of the researcher will be to set up path integral molecular dynamics on a Ca2+-H2O system, with empirical potentials (with the CP2K code), in order to compute Ca isotopes fractionation properties for this system. This will be first realized with empirical potentials, then with an ab initio approach. Depending on the avancement, another task of the postdoc may be to realize some calculations on solids, based on the well-controlled approach based on the harmonic approximation.

For further information about the project, please contact:
Merlin Méheut : [email protected]
To apply for this position, please connect to the following link : https://bit.ly/3oo5NyI

CV and motivation letter will be requested.

Required technical skills:
- Use of ab initio molecular dynamics codes: CP2K, CPMD, CP, PINY-MD. Good level.
- Possibly expertise to build empirical potentials by inverse Monte Carlo approach.
- Possibly experience in path integral molecular dynamics.

Knowledge to put in application:
- Operating molecular dynamics algorithms
- Path integral formulation of quantum mechanics.

Know-how :
- Computer programing : good level
- Developing a scientific approach to set up a methodology aiming at reproducing a quantity measured experimentally.
- Estimating the different sources of error and their consequences on the final result.

Some papers in relation to the proposed work::
Dupuis R., Benoît M, Tuckerman M, Méheut M. (2017), Accounts of chemical research 50 (7), 1597-1605
Méheut M. and Schauble E.S. (2014), Geochimica et Cosmochimica Acta 134, 137-154