Abstract:
Variational calculations employing explicitly correlated Gaussian functions and explicitly including the
nuclear motion [i.e., without assuming the Born-Oppenheimer (BO) approximation] have been performed
to determine the lowest singlet transition energy in the 9Be atom. The non-BO wave functions were used
to calculate the 2 relativistic corrections ( 1=137:035 999 679). With those corrections and with the
3 and 4 QED corrections determined previously by others, we obtained 54 677:35 cm 1 for the 31S !
21S transition energy. This result falls within the error bracket for the experimental transition of
54 677:26 10 cm 1. This is the first time an electronic transition of Be has been calculated from first
principles with the experimental accuracy