  Inelastic neutron scattering (INS) spectra of hydrogen in face-centered cubic
palladium have been calculated considering nuclear quantum effects (NQE) at
finite temperatures. The calculations were performed using semiclassical
Brownian chain molecular dynamics (MD) [Shiga, J. Comput. Chem. 43, 1864
(2022)] and artificial neural network potentials with an accuracy of
generalized gradient approximation of density functional theory. The calculated
spectra are in good agreement with experimental spectra with respect to the
peak positions and intensities corresponding to the fundamental tone and the
first overtone of the vibrational excitation of hydrogen atoms. These results
differ significantly from those of classical MD, indicating that NQE plays an
essential role in the correct estimation of the INS spectrum. Importantly, the
NQE acts as a blue-shift of the INS spectrum for hydrogen in the octahedral
site, due to strong anharmonic vibrations of hydrogen on the potential surface
with even symmetry. The calculated peak shifts associated with Pd lattice
distortion were also in agreement with experimental results.
