Accurately solving the electronic Schrodinger equation of atoms and molecules using explicitly correlated (r12-)MR-CI.: The ground state of beryllium dimer (Be2)

The recently proposed (explicitly correlated) r(12)-MR-ACPF method is applied to the ground state (X(1)Sigma(g)(+)) potential of Be-2. A large [19s11p6d4f3g2h] basis set and a valence-CAS reference space (60 CSFs) are used. At long range, the reference space is augmented by {3s,3p} orbitals (568 CSFs). The calculated dissociation energy (898 +/- 8 cm(-1)) is considerably larger than the experimental estimate (790 +/- 30 cm(-1)). The other molecular constants, however, are in good agreement. Our potential is close to the one calculated by Starck and Meyer. (C) 1999 Elsevier Science B.V. All rights reserved.