Energy levels of many-valence-electron atomic (ionic) systems play an impor
tant role in many scientific disciplines. Many theoretical methods to calcu
late the energy levels of Rydberg states of atoms and ions have been provid
ed, and the carbon group atoms have been treated. In this paper, we compute
d single excited states of carbon group atoms with high precision. The accu
racy of most of our results that have been reached are less than 1 cm(-1).
This is quite good among all the present theoretical methods. (C) 2000 Amer
ican Institute of Physics. [S0021-9606(00)30629-8].