DFT calculations on single lanthanide atoms: Is the task as simple as it seems?

Abstract

We tested three spin-unconstrained DFT calculation schemes (PBE-D2/DNP theoretical level with DSPP and ECP pseudopotentials within DMol³ module, and PBE-D2/def2-ECP within TURBOMOLE package) to verify which of them allows for the successful single-point calculations on the full series of isolated lanthanide atoms (La to Lu), and compared the basic electronic characteristics obtained such as spin values (that is, the number of unpaired electrons), spin density plots, HOMO-LUMO plots, and the gap energies. A number of serious problems were found with TURBOMOLE (impossibility of calculations for Tm and Lu; unrealistic spin values for La, Eu and Tb), but a fractional orbital occupancy was never detected at the target thermal smearing value of 0.0001 Ha. When employing DMol³, the full set can be completed with DSPP; with ECP, with the exception of Tb. However, in some cases a fractional orbital occupancy was detected.