We present a detailed bifurcation structure and associated flow patterns for
low-Prandtl number (P=0.0002,0.002,0.005,0.02) Rayleigh-B\'{e}nard
convection near its onset. We use both direct numerical simulations and a
30-mode low-dimensional model for this study. We observe that low-Prandtl
number (low-P) convection exhibits similar patterns and chaos as zero-P
convection \cite{pal:2009}, namely squares, asymmetric squares, oscillating
asymmetric squares, relaxation oscillations, and chaos. At the onset of
convection, low-P convective flows have stationary 2D rolls and associated
stationary and oscillatory asymmetric squares in contrast to zero-P convection
where chaos appears at the onset itself. The range of Rayleigh number for which
stationary 2D rolls exist decreases rapidly with decreasing Prandtl number. Our
results are in qualitative agreement with results reported earlier
