High-Pressure Chemistry

My research on electrides focuses on understanding how electrons localize in interstitial regions of compressed materials. Through studies of lithium, sodium, calcium, and related systems under extreme conditions, I developed bonding frameworks based on multicenter interactions that explain the emergence of these unconventional electronic states. This work connects quantum chemistry concepts with the design of functional materials for catalysis, superconductivity, and energy applications.

• Storm, C. V.; Racioppi, S.; Duff, M. J.; McHardy, J. D.; Zurek, E.; McMahon, M. I. Experimental Evidence of Interstitial Electron Density in Transparent Dense Sodium. Commun. Mater., 2025, 6, 201. DOI
• Racioppi, S.; Zurek, E. High-Pressure Electrides: A Quantum Chemical Perspective. Annu. Rev. Mater. Res., 2025, 55, 421-442. DOI
• Racioppi, S.; Zurek, E. Looking at High-Pressure Electrides Through the Lens of Quantum Crystallography: The Case of Simple Cubic Calcium. Acta Cryst., 2025, B81. DOI
• Racioppi, S.; Storm, C. V.; McMahon, M. I.; Zurek, E. On the Electride Nature of Na-hP4. Angew. Chem. Int. Ed., 2023, e202310802. DOI

I investigate how helium, traditionally considered chemically inert, can stabilize unexpected compounds and host-guest structures under pressure. My work explores how helium incorporation modifies bonding, compressibility, and structural stability, leading to new classes of materials. These studies provide insight into high-pressure chemistry relevant to planetary interiors and advanced materials design.

• Weadock, N.; Holle, W.; Myford, K.; Racioppi, S.; Ghimire, A.; Ladd, D.; Park, C.; Zurek, E.; Toney, M.; Bridges, F.; Deemyad, S. Pressure-driven helium insertion for structural stability of CH3NH3PbBr3 hybrid perovskites. Chem. Mater., 2026. DOI
• Racioppi, S.; Miao, M.; Zurek, E. Intercalating Helium into A-site Vacant Perovskites. Chem. Mater., 2023, 35, 4297-4310. DOI

A central theme of my research is understanding how compression activates semicore and core electrons into chemical bonding. Under extreme pressure, orbital hierarchies collapse and elements exhibit entirely new chemical behavior. By combining electronic-structure and orbital theory, I study how these effects reshape the periodic trends.

• Racioppi, S.; Zurek, E. Activation of Semicore Electrons in Alkali Metals and Their Role in the B1–B2 Phase Transition under Pressure. J. Am. Chem. Soc., 2025, 147, 5, 32745-32751. DOI

My work bridges theoretical predictions with experimental observations obtained under extreme conditions. I collaborate closely with high-pressure experimental groups, combining first-principles simulations with diffraction, spectroscopy, and dynamic compression measurements to interpret complex datasets. This integrated approach allows direct validation of theoretical models and accelerates the discovery of novel materials at high pressure.

• Racioppi, S.; De la Roza, A.; Hajinazar, S.; Zurek, E. Powder X-Ray Diffraction Assisted Evolutionary Algorithm for Crystal Structure Prediction. Digit. Discov., 2025, 4, 73-83. DOI
• Racioppi, S.; Zurek, E. Using Topology to Predict Electrides in the Solid State. J. Phys. Chem. A, 2025, 129, 10031−10038. DOI

I use computational materials design to search for and understand superconductors under pressure, with particular interest in pure metals and hydrogen-rich compounds. My research investigates how bonding, electronic structure, and lattice dynamics cooperate to produce superconductivity at elevated temperatures. By linking chemical intuition with predictive simulations, I aim to identify guiding principles for next-generation superconducting materials.

• Racioppi, S.; Saffarin-Deemyad, I.; Holle, W.; Belli, F.; Ferry, R.; Kenney-Benson, C.; Smith, C. J.; Zurek, E.; Deemyad, S. Lithium's low-temperature phase transitions: Insights into quantum lattice dynamics and superconductivity. Phys. Rev. B, 2025, 111, 054111. DOI
• Caussé, M.; Bozier, K.; Cooke, P. I. C.; Racioppi, S.; Pickard, C. J. Metastability and high-Tc superconductivity in A15-type ternary hydride YSbH6 at moderate pressure. Phys. Rev. B, 2026. DOI