The Rayleigh–Benard Convection (RBC) were studied theoretically in the homeotropic nematic liquid
crystal (NLC) cell due to the absorption of a normally incident Gaussian light beam from upper side of
the cell. It was shown that a convection of hydrodynamic motion in the NLC can be induced and eventually the molecular director coupling with hydrodynamics reorients the director. An external magnetic
field parallel to the director decreases the director reorientation and the radial flow velocity, while the
velocity in the z direction is unaffected. The results were found to be in a range that can easily be checked
experimentally