Application of the valence‐universal coupled‐cluster method based on various model spaces to 1S states of Be

Abstract

AbstractThe recently formulated atomically oriented valence‐universal theory (VU–CCSD/R) based on various complete model spaces is applied to the accurate description of the 2s2 1S, 2s3s 1S, 2p2 1S, and 3s2 1S states of Be. Two extensive 9s9p7d7f5g STO basis sets that differ by one s‐type function are employed. Both standard and nonstandard solutions of the VU–CC equations are considered. The eight values of the ground‐state energies obtained when considering various model spaces and basis sets were found to differ very little. The energies of the individual excited states disclosed a relatively weak dependence on the choice of model spaces defining the method (or, equivalently, on the fact whether they correspond to standard or nonstandard solutions). In turn, the energies of the excited states strongly depend on the STO basis set used in the calculations. To obtain a reliable description of both the ground state and excited states, well‐balanced STO basis sets have to be employed. © 1995 John Wiley & Sons, Inc.