Relativistic effects on geometry and electronic structure of small Pu_n species (n= 1,2,4)

Relativistic effects on the properties of small neutral Pd_n species (n = 1,2,4) and Pd₂ have been examined for the first time at the all-electron level by performing scalar-relativistic and nonrelativistic density functional calculations using a gradient-corrected density functional. Relativistic effects are found to be important: They lead to a contraction of bond lengths, increase of vibrational frequencies, and a significant enhancement of binding energies. While relativistic effects are quite uniform for several states of Pd₄, they vary for the states examined for Pd₂, leading to a change of ground state due to relativity. The calculated relativistic properties of Pd, and Pd₂ are in good agreement with available experimental data from mass spectrometry and photoelectron spectroscopy. For Pd₄ three-dimensional structures are found to be preferred to planar ones and many nearly isoenergetic isomers exist.