Variational study of the two-temperature model parameters based on finite volume method for unraveling ultrafast reaction dynamics on Pd(100) surface

The well-known two-temperature model (TTM) is a valuable framework for investigating ultrafast energy transfer processes in metallic systems. While femtosecond laser-induced heterogeneous surface chemical dynamics, such as photo-desorption from single-crystal surfaces, have been successfully studied and modeled for several systems, clear guidelines for systematically tuning individual TTM parameters are still lacking. In this work, we present a systematic variational study of key TTM parameters, including laser fluence (F) between 10 and 100 J m−2, activation energy (Ea) associated with surface reactions (0.5–4.0 eV), thermal conductivity (κ) in the range of 10–100 W m−1 K−1, and the vibrational frequency of the adsorbate along the reaction coordinate (νrc) within its characteristic domain. Furthermore, the interplay between two dominant energy transfer channels is examined by varying the electron–adsorbate coupling constant (ηel) and the electron–phonon coupling constant (g). A finite volume method-based numerical implementation of TTM is developed to reproduce previously reported experimental results. Our analysis demonstrates a twofold dependence of energy flow on the competition between ηel and g. To the best of our knowledge, this is the first comprehensive study that explores the full parametric space of TTM and prescribes a systematic approach for coupling TTM-based simulations with experimental observations.