Velocity correlations in liquid hydrogen fluoride

The center-of-mass velocity autocorrelation function is analyzed by computer simulation in a model of liquid hydrogen fluoride at two state points. In comparison with water (another hydrogen-bonded liquid) new features arise. To understand the peculiarities of HF, we have investigated atomic velocity correlations in both the laboratory and a molecular frame. The comparison of the frequency spectra permits to ascertain the role of fluorine-hydrogen correlations (or of rototranslational couplings) in the center-of-mass velocity autocorrelation function. At low temperature, the appearance of a long time tail is discussed in terms of projections in the two references frames, and found to be mostly associated with orientational correlations. A discussion in terms of velocity transfer between nearest-neighbor molecules is also given. (C) 1999 American Institute of Physics. [S0021-9606(99)52034-5].