  We perform density functional theory calculations using Gaussian
atomic-orbital methods within the generalized gradient approximation for the
exchange and correlation to study the interactions in the bare and hydrogenated
platinum clusters. The minimum-energy structures, binding energies, relative
stabilities, vibrational frequencies and the highest occupied and lowest
unoccupied molecular-orbital gaps of Pt_nH_m (n=1-5, m=0-2) clusters are
calculated and compared with previously studied pure platinum and hydrogenated
platinum clusters. We investigate any magic behavior in hydrogenated platinum
clusters and find that Pt_4H_2 is more stable than its neighboring sizes. Our
results do not agree with a previous conclusion that 3D geometries of Pt
tetramer and pentamer are unfavored. On the contrary, the lowest energy
structure of Pt_4 is found to be a distorted tetrahedron and that of Pt_5 is
found to be a bridge site capped tetrahedron which is a new global minimum for
Pt_5 cluster. The successive addition of H atoms to Pt_n clusters leads to an
oscillatory change in the magnetic moment of Pt_3 - Pt_5 clusters.
