Accurate calculations of dissociation energies of weakly bonded He2 and Be2 molecules by MRCI method

Abstract

The He2 and Be2 ground state potential curves have been calculated by extrapolating to an infinite basis BSSE corrected MRCI total energies obtained with large Gaussian basis sets, large reference configuration spaces, and pseudo-natural molecular orbitals. The calculated De = 11.0031 K and Re = 5.607 a.u. of He2 are in an excellent agreement with De = 11.006 ± 0.004 K and Re = 5.608 ± 0.012 a.u. obtained recently by SAPT with SM energy correction. The obtained Be2 non-relativistic De = 822 cm−1 and relativistically corrected De = 818 cm−1 are in a good agreement with experimental De = 790 ± 30 cm−1 and the value of 829 ± 64 cm−1 obtained recently by a quantum Monte Carlo method.