Accurate and Scalable Quantum Hydrodynamic Simulations of Plasmonic Nanostructures Within OFDFT

Quantum hydrodynamic theory (QHT) provides a computationally efficient alternative to time-dependent density functional theory for simulating plasmonic nanostructures, but its predictive power depends critically on the choice of ground-state electron density and energy functional. We present OF-PGSLN, a scalable and accurate QHT framework that integrates orbital-free (OF) density functional theory with a Laplacian-level kinetic energy functional (PGSLN). We calibrate the model using density functional theory and time-dependent density functional theory for sodium jellium nanospheres, determining optimal parameters to reproduce both ground-state density and localized surface plasmon resonances. Our results show that OF-PGSLN accurately captures the size-dependent localized surface plasmon energies and oscillator strengths with less computational cost. We further apply the method to sodium nanodimers and find that the commonly used linear superposition of single-sphere density becomes inaccurate at sub-nanometer gaps. In contrast, OF-PGSLN captures critical interaction-induced changes in electron density and optical response. This approach overcomes key limitations of existing QHT models by enabling accurate and stable simulations for arbitrary nanostructures beyond simple geometries. Overall, OF-PGSLN provides a scalable, accurate, and generalizable framework for quantum plasmonic simulations, offering a powerful tool for modeling complex nanostructures.