Dynamical Ordering of Hydrogen Molecules Induced by Heat Flux

Achieving a direct nonequilibrium simulation for hydrogen systems has been quite challenging because nuclear quantum effects (NQEs) have to be taken into account. We directly simulated nonequilibrium hydrogen molecules under a temperature gradient with the recently developed nonempirical molecular dynamics method, which describes nonspherical hydrogen molecules with the NQEs. We found dynamical ordering purely induced by heat flux, which should be distinguished from static ordering like orientational alignment, as decelerated translational motions and enhanced intensity of H-H vibrational power spectra despite the little structural ordering. This dynamical ordering, which was enhanced with stronger heat flux while independent of system size, can be regarded as self-solidification of hydrogen molecules for their efficient heat conduction.