  The UV-visible and IR properties of the Cu$_{38}$ nanocluster depend to a
great extent on the temperature. Density functional theory and
nanothermodynamics can be combined to compute the geometrical optimization of
isomers and their spectroscopic properties in an approximate manner. In this
article, we investigate entropy-driven isomer distributions of Cu$_{38}$
clusters and the effect of temperature on their UV-visible and IR spectra. An
extensive, systematic global search is performed on the potential and free
energy surfaces of Cu38 using a two-stage strategy to identify the
lowest-energy structure and its low-energy neighbors. The effects of
temperature on the UV and IR spectra are considered via Boltzmann probability.
The computed UV-visible and IR spectrum of each isomer is multiplied by its
corresponding Boltzmann weight at finite temperature. Then, they are summed
together to produce a final temperature-dependent, Boltzmann-weighted
UV-visible and IR spectrum. Additionally, Molecular Dynamics simulation of the
Cu$_{38}$ nanocluster was performed to gain insight into the system dynamics
and make a three-dimensional movie of the system with atomistic resolution. Our
results show the thermal populations at the absolute temperature of Cu38
cluster, and the disordered structure that dominates at high temperatures.
