  We study the optical force arising when isolated gold nanowire pairs and
metamaterials with a gold nanowire pair in the unit cell are illuminated with
laser radiation. Firstly, we show that isolated nanowire pairs are subject to
much stronger optical forces than nanospheres due to their stronger electric
and magnetic dipole resonances. We also investigate the properties of the
optical force as a function of the length of the nanowires and of the distance
between the nanowires. Secondly, we study the optical force in a metamaterial
that consists of a periodic array of nanowire pairs. We show that the ratio of
the size of the unit cell to the length of the nanowires determines whether the
electric dipole resonance leads to an attractive or a repulsive force, and we
present the underlying physical mechanism for this effect.
