ELECTRONIC-STRUCTURE CRITICAL PARAMETERS FOR THE LITHIUM ISOELECTRONIC SERIES

The finite-size scaling method is used to calculate the critical param eters for the lithium isoelectronic series. The critical nuclear charg e, which is the minimum charge necessary to bind three electrons, for the ground state was found to be Z(c) similar or equal to 2. Results s how that the analytical behavior of the energy as a function of the nu clear charge for lithium is completely different from that of helium. Analogy with standard phase transitions show that for helium, the tran sition from a bound state to a continuum is ''first order,'' while lit hium exhibits a ''second order phase transition.''.