Geometries and energy separations of 24 low-lying electronic states of Pb 5 with different structures are investigated employing the complete active space multiconfiguration self-consistent-field method (CASSCF) followed by multi-reference singles + doubles configuration interaction (MRSDCI) and the relativistic configuration interaction (RCI) computations that included up to 3.0 million configurations. The 1 A 1 electronic state with trigonal bipyramidal (D 3 h ) geometry is the ground state of Pb 5 , but it is mixed with triplet states about 8% due to spin-orbit coupling.