Effects on spectroscopic parameters of several low-lying electronic states of GeS by core-valence correlation and relativistic corrections

► Effect on the PECs by the core-valence correlation and relativistic corrections is considered. ► The PECs obtained by the MRCI and MRCI+Q are extrapolated to the CBS limit. ► The extrapolation obviously improves the spectroscopic parameter quality. ► The spectroscopic parameters extrapolated to the CBS limit achieve much high accuracy. ► The effect on the spectroscopic parameters by the nonadiabatic correction is very small.