Materials Scientist
Geochemistry Group
Materials Scientist
Geochemistry Group


Michel Sassi obtained his Ph.D. in France in 2010 from Aix-Marseille University where his research focused on quantifying inter-molecular and molecule-substrate interactions of self-assembled 2-D molecular films adsorbed on metallic substrates. From 2010 to 2014, Dr. Sassi joined the Nanochemistry Research Institute (NRI) at Curtin University (Perth, Western Australia, Australia) where his research focused on developing a fundamental understanding of the effects of radioactive decay in nuclear-related materials and small (bio)molecules. This led him to develop a unique way of using first-principles simulations to understand and predict the physical, chemical, and structural consequences of radionuclide transmutation following radioactive decay. In 2014, Dr. Sassi joined PNNL and has been providing expertise in the areas of interface chemistry, earth, and nuclear materials science. Dr. Sassi is a versatile computational expert who has built his reputation by solving interdisciplinary problems in chemistry, physics, geochemistry, environmental, nuclear, and materials science.

His research is centered on developing a fundamental understanding of the chemical and physical processes that drive the properties of diverse materials, and how these processes affect their interactions with the environment. In the geochemistry area, Dr. Sassi employs ab initio simulations to investigate the reactivity at the mineral-fluid interface encompassing molecular adsorption, surface configuration and defects, as well as determining the structure, relative thermodynamics, and phase transitions between different mineral phases. In nuclear materials related areas, his research focuses on understanding radiation-induced defects, microstructure evolution, quantification of the effect of radioactive transmutation in condensed matter and molecules, and chemical kinetics.

Research Interest

  • Develop a fundamental understanding of the physical and chemical processes involved in (nano)minerals and nuclear materials.
  • Chemical and structural consequences of radioactive decay in nuclear materials and molecules.
  • Radiation-induced defects, microstructure evolution.
  • Surface reactivity and ab initio thermodynamics of bulk phase materials.
  • Prediction of bulk material phases based on composition and transition pathways.
  • Simulation of X-ray spectra (XMCD, XANES, EXAFS) for material characterization and defect quantification.
  • Simulation of phonon, IR, Raman, and Sum Frequency Generation (SFG) spectra for bulk and surface characterization.
  • Ab initio numerical simulations.
  • Chemical kinetics.


  • Ph.D. in Physics and Materials Science, Aix-Marseille University
  • M.S. in Physics, Aix-Marseille University
  • B.S. in Physics, Aix-Marseille University

Affiliations and Professional Service

  • Member, American Chemical Society
  • Peer Reviewer, Chemistry of Materials (ACS), Environmental Science & Technology (ACS), The Journal of Physical Chemistry C (ACS), Scientific Reports (NPG), Applied Surface Science (Elsevier), Clays and Clay Minerals (Springer Nature), Minerals (MDPI), Materials (MDPI), Condensed Matter (MDPI), Journal of Synchrotron Radiation (IUCr), Physical Review B (APS), Physical Chemistry Chemical Physics (RSC), Geochimica et Cosmochimica Acta (Elsevier)



  • Burton A., R. Paudel, B.E. Matthews, M. Sassi, S.R. Spurgeon, B.H. Farnum, and R.B. Comes. 2022. "Thickness Dependent OER Electrocatalysis of Epitaxial LaFeO3 Thin Films." Journal of Materials Chemistry A 10, no. 4:1909–1918. PNNL-SA-164824. doi:10.1039/D1TA07142D
  • Liu L., J. Chun, X. Zhang, M. Sassi, A.G. Stack, C.I. Pearce, S.B. Clark, K.M. Rosso, J.J. De Yoreo, and G.A. Kimmel. 2022. "Radiolysis and Radiation-Driven Dynamics of Boehmite Dissolution Observed by In Situ Liquid-Phase TEM." Environmental Science & Technology 56, no. 8:5029-5036. PNNL-SA-169258. doi:10.1021/acs.est.1c08415
  • Sassi M., and K.M. Rosso. 2022. "Ab Initio Evaluation of Solid-State Transformation Pathways from Ferrihydrite to Goethite." ACS Earth and Space Chemistry 6, no. 3:800–809. PNNL-SA-169622. doi:10.1021/acsearthspacechem.2c00026
  • Sassi M., S.R. Spurgeon, B.E. Matthews, A. Devaraj, and D.J. Senor. 2022. "First-principles study of tritium trapping in γ-LiAlO2 nanovoids." Journal of Physical Chemistry C 126, no. 12:5767–5776. PNNL-SA-169629. doi:10.1021/acs.jpcc.2c00381


  • Matthews B.E., M. Sassi, C.M. Barr, C. Ophus, T.C. Kaspar, W. Jiang, and K. Hattar, et al. 2021. "Percolation of Ion-Irradiation-Induced Disorder in Complex Oxide Interfaces." Nano Letters 21, no. 12:53535359. PNNL-SA-161595. doi:10.1021/acs.nanolett.1c01651
  • Sassi M., A.M. Chaka, and K.M. Rosso. 2021. "Ab Initio Thermodynamics Reveals the Nanocomposite Structure of Ferrihydrite." Communications Chemistry 4, no. 1:134. PNNL-SA-164602. doi:10.1038/s42004-021-00562-7
  • Sassi M., and D.J. Senor. 2021. Tritium Diffusion in Fe-Al Aluminide Coating Bulk Phases. PNNL-32040. Richland, WA: Pacific Northwest National Laboratory


  • Bilbrey J.A., C.M. Ortiz Marrero, M. Sassi, A.M. Ritzmann, N.J. Henson, and M. Schram. 2020. "Tracking the chemical evolution of iodine species using recurrent neural networks." ACS Omega 5, no. 9:45884594. PNNL-SA-148824. doi:10.1021/acsomega.9b04104
  • Henson N.J., M. Sassi, A.M. Ritzmann, S.E. Muller, and A.E. Johnson. 2020. Chemical Modeling of the Capture of Radioiodine Species. PNNL-30371. Richland, WA: Pacific Northwest National Laboratory. Chemical Modeling of the Capture of Radioiodine Species
  • Sassi M., A. Devaraj, S.R. Spurgeon, B.E. Matthews, and D.J. Senor. 2020. First Principles Modeling of Tritium Trapping in gamma-LiAlO2 Nanovoids. PNNL-30529. Richland, WA: Pacific Northwest National Laboratory
  • Sassi M., A.M. Ritzmann, and N.J. Henson. 2020. "Consequences of 131I transmutation in gas phase radioiodine molecules and adsorbed on graphite surface." Journal of Physical Chemistry C 124, no. 39:2146121466. PNNL-SA-153560. doi:10.1021/acs.jpcc.0c05928
  • Sassi M., E.D. Walter, O. Qafoku, K.M. Rosso, and Z. Wang. 2020. "Radiation-induced interfacial hydroxyl transformation on boehmite and gibbsite basal surfaces." Journal of Physical Chemistry C 124, no. 40:2218522191. PNNL-SA-153541. doi:10.1021/acs.jpcc.0c06844
  • Sassi M., Z. Wang, E.D. Walter, X. Zhang, H. Zhang, X.S. Li, and A. Tuladhar, et al. 2020. "Surface Hydration and Hydroxyl Configurations of Gibbsite and Boehmite Nanoplates." Journal of Physical Chemistry C 124, no. 9:52755285. PNNL-SA-149815. doi:10.1021/acs.jpcc.0c00659
  • Simonnin P., M. Sassi, B. Gilbert, L. Charlet, and K.M. Rosso. 2020. "Phase Transition and Liquid-like Superionic Conduction in Ag2S." Journal of Physical Chemistry C 124, no. 18:1015010158. PNNL-SA-152823. doi:10.1021/acs.jpcc.0c00260
  • Spurgeon S.R., T.C. Kaspar, V. Shutthanandan, J. Gigax, L. Shao, M. Sassi. 2020. “Asymmetric Lattice Disorder Induced at Oxide Interfaces.” Advanced Materials Interfaces 7, no. 8:1901944. doi:10.1002/admi.201901944
  • Walter E.D., K.C. Schwarz, S. Anil Kumar, Y. Chen, M. Sassi, Z. Wang, and K.M. Rosso. 2020. "Evolution of Radicals from the Photolysis of High Ionic Strength Alkaline Nitrite Solutions." Journal of Physical Chemistry A 124, no. 16:30193025. PNNL-SA-150363. doi:10.1021/acs.jpca.9b11438
  • Wang Z., E.D. Walter, M. Sassi, X. Zhang, H. Zhang, S. Li, and Y. Chen, et al. 2020. "The role of surface hydroxyls on the radiolysis of gibbsite and boehmite nanoplatelets." Journal of Hazardous Materials 398. PNNL-SA-150311. doi:10.1016/j.jhazmat.2020.122853


  • Bagus P.S., M. Sassi, and K.M. Rosso. 2019. "Cluster Embedding of Ionic Systems: Point Charges and Extended Ions." Journal of Chemical Physics 151, no. 4:044107. PNNL-SA-147745. doi:10.1063/1.5108728
  • Notini L., D. Latta, A. Neumann, C.I. Pearce, M. Sassi, A.T. N'Diaye, and K.M. Rosso, et al. 2019. "A Closer Look at Fe(II) Passivation of Goethite." ACS Earth and Space Chemistry 3, no. 12:27172725. PNNL-SA-150749. doi:10.1021/acsearthspacechem.9b00224
  • Sassi M., and K.M. Rosso. 2019. "Reply to "Comment on ‘Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles'"." ACS Earth and Space Chemistry 3, no. 8:15811583. PNNL-SA-147743. doi:10.1021/acsearthspacechem.9b00160
  • Sassi M., and K.M. Rosso. 2019. "Roles of Hydration and Magnetism on the Structure of Ferrihydrite from First Principles." ACS Earth and Space Chemistry 3, no. 1:7078. PNNL-SA-142092. doi:10.1021/acsearthspacechem.8b00138
  • Sassi M., T.C. Kaspar, K.M. Rosso, and S.R. Spurgeon. 2019. "Effect of structure and composition on the electronic excitation induced amorphization of La2Ti2-xZrxO7 ceramics." Scientific Reports 9, no. 1:Article No. 8190. PNNL-SA-139722. doi:10.1038/s41598-019-44621-5
  • Spurgeon S.R., M. Sassi, C. Ophus, J. Stubbs, E.S. Ilton, and E.C. Buck. 2019. "Nanoscale Oxygen Defect Gradients in UO2+x Surfaces." Proceedings of the National Academy of Sciences of the United States of America 116, no. 35:1718117186. PNNL-SA-141717. doi:10.1073/pnas.1905056116


  • Bagus P.S., C.J. Nelin, M. Sassi, E.S. Ilton, and K.M. Rosso. 2018. "Consequences of Realistic Embedding for the L2,3 Edge XAS of a-Fe2O3." Physical Chemistry Chemical Physics. PCCP 20, no. 6:43964403. PNNL-SA-131666. doi:10.1039/c7cp06926j
  • Notini L., D. Latta, A. Neumann, C.I. Pearce, M. Sassi, A.T. N'Diaye, and K.M. Rosso, et al. 2018. "The role of defects in Fe(II) - goethite electron transfer." Environmental Science & Technology 52, no. 5:27512759. PNNL-SA-131667. doi:10.1021/acs.est.7b05772
  • Okumura M., S.N. Kerisit, I. Bourg, L.N. Lammers, T. Ikeda, M. Sassi, and K.M. Rosso, et al. 2018. "Radiocesium interaction with clay minerals: Theory and simulation advances Post-Fukushima." Journal of Environmental Radioactivity 189. PNNL-SA-137174. doi:10.1016/j.jenvrad.2018.03.011
  • Stifler C., N. Kollin Wittig, M. Sassi, C. Sun, M.A. Marcus, H. Birkedal, and E. Beniash, et al. 2018. "X-ray Linear Dichroism in Apatite." Journal of the American Chemical Society 140, no. 37:1169811704. PNNL-SA-131664. doi:10.1021/jacs.8b05547


  • Sassi M., K.M. Rosso, M. Okumura, M. Machida. 2017. “Reply To Comments On Radiation-damage Resistance In Phyllosilicate Minerals From First Principles And Implications For Radiocesium And Strontium Retention In Soils”. Clays and Clay Minerals 65, no. 5:371375. doi:10.1346/CCMN.2017.064078
  • Bagus P.S., C.J. Nelin, E.S. Ilton, M. Sassi, and K.M. Rosso. 2017. "Analysis of X-ray adsorption edges: L2,3 edge of FeCl4-." Journal of Chemical Physics 147, no. 22:Article No. 224306. PNNL-SA-131505. doi:10.1063/1.5006223
  • Okumura M., M. Sassi, K.M. Rosso, and M. Machida. 2017. "Origin of 6-fold Coordinated Aluminum at (010)-type Pyrophyllite Edges." AIP Advances 7, no. 5:055211. PNNL-SA-153406. doi:10.1063/1.4983213
  • Sassi M., C.I. Pearce, P.S. Bagus, E. Arenholz, and K.M. Rosso. 2017. "First-Principles Fe L2,3-Edge and O K-Edge XANES and XMCD Spectra for Iron Oxides." Journal of Physical Chemistry A 121, no. 40:76137618. PNNL-SA-131673. doi:10.1021/acs.jpca.7b08392
  • Sassi M., M. Okumura, M. Machida, and K.M. Rosso. 2017. "Transmutation effects on long-term Cs retention in phyllosilicate minerals from first principles." Physical Chemistry Chemical Physics. PCCP 19, no. 39:2700727014. PNNL-SA-131843. doi:10.1039/c7cp04496h


  • Sassi M., K.M. Rosso, M. Okumura, and M. Machida. 2016. "Radiation-Damage Resistance in Phyllosilicate Minerals from First Principles and Implications for Radiocesium and Strontium Retention in Soils." Clays and Clay Minerals 64, no. 2:108114. PNNL-SA-113803. doi:10.1346/CCMN.2016.0640203


  • Bagus P.S., M. Sassi, and K.M. Rosso. 2015. "Intermediate Coupling For Core-Level Excited States: Consequences For X-Ray Absorption Spectroscopy." Journal of Electron Spectroscopy and Related Phenomena 200. PNNL-SA-108070. doi:10.1016/j.elspec.2015.04.021
  • Wen H., M. Sassi, Z. Luo, C. Adamo, D. Schlom, K.M. Rosso, and X. Zhang. 2015. "Capturing ultrafast photoinduced local structural distortions of BiFeO3." Scientific Reports 5. PNNL-SA-110895. doi:10.1038/srep15098