  We theoretically study the effects of dynamical lattice distortion in a
three-dimensional Rashba system based on a tight-binding model. Considering an
$sp$-electron system on a tetragonal lattice with broken inversion symmetry,
lattice distortions are incorporated through hopping-integral and crystal-axis
modulations. The effective Hamiltonian for the $p_z$- or $s$-derived band is
found to have Rashba modulation terms, which induce various types of spin
currents, such as Rashba, quadrupolar, perpendicular, and helicity currents.
The results are compared with those obtained by the method of local coordinate
transformation.
