  Using molecular dynamics simulations, we show that free diffusion of a
nanoscale particle (molecule) with asymmetric structure critically depends on
the orientation in a finite timescale of picoseconds to nanoseconds. In a
timescale of ~100 ps, there are ~10% more possibilities for the particle moving
along the initial orientation than moving opposite to the orientation; and the
diffusion distances of the particle reach ~1 nm. We find that the key to this
observation is the orientation-dependence of the damping force to the moving of
the nanoscale particle and a finite time is required to regulate the particle
orientation. This finding extends the work of Einstein to nano-world beyond
random Brownian motion, thus will have a critical role in the understanding of
the nanoscale world.
