Microscopic dynamics of hard ellipsoids in their liquid and glassy phase

Abstract

To investigate the influence of orientational degrees of freedom on the dynamics of molecular systems in the supercooled and glassy regime we have solved numerically the mode-coupling equations for hard ellipsoids of revolution. For a wide range of volume fractions φ and aspect ratios x 0 we find an orientational peak in the center of mass spectra χ 0 0 0 ″(q,ω) and φ 0 0 0 ″(q,ω) about one decade below a high-frequency peak. This orientational peak is the counterpart of a peak appearing in the quadrupolar spectra χ 2 2 m ″(q,ω) and φ 2 2 m ″(q,ω) . The latter peak is almost insensitive to φ for x 0 close to one, i.e., for weak steric hindrance, and broadens strongly with increasing x 0. Deep in the glass we find an additional peak between the orientational and the high-frequency peak. We have evidence that this intermediate peak is the result of a coupling between modes with l=0 and l=2, due to the non-diagonality of the static correlators.