A Two-Band Model for Electron Screening in Pd, Ti, Cu, Ag, and Au: Resolving the Noble Metal Exception

The Debye plasma model reproduces the electron screening potentials of most metals but fails on the noble metals Cu, Ag, and Au, predicting screening potentials of 290–350 eV where measurements show essentially zero. This exception has remained unexplained for two decades. We present a two-band screening model that separates the s-p conduction channel from the d-band channel, with a d-band filling factor that modulates the s-p contribution. The model reproduces the published sigmoid screening curves for Pd, PdD, Ti, and TiD from Karahadian et al. (2026) with an RMS residual of 0.243 keV. With the same global parameters, and setting for the noble metals, the model predicts eV for Cu, Ag, and Au, consistent with the observed upper bound of approximately eV. The fitted d-band filling factors are for Pd and Ti. One additional parameter—physically interpretable as the d-band filling factor—resolves the noble metal exception for Cu, Ag, and Au while preserving the transition-metal fits. The classification of group-4 elements (Ti, Zr, Hf) remains an open question, because the Raiola and Karahadian measurements disagree on whether these elements show large or small screening. The model is presented as an Amaterasu-layer effective description built on the Ouroboros v10 field framework. r—physically interpretable as the d-band filling factor—resolves the noble metal exception for Cu, Ag, and Au while preserving the transition-metal fits. The classification of group-4 elements (Ti, Zr, Hf) remains an open question, because the Raiola and Karahadian measurements disagree on whether these elements show large or small screening. The model is presented as an Amaterasu-layer effective description built on the Ouroboros v10 field framework.