Nonorthogonal configuration interaction study of the ground state of BeH2

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Abstract
A series of configuration interaction (CI) calculations are carried out on the 1 Σ g + ground state of the BeH2 molecule using a nonorthogonal one‐electron basis of elementary symmetry orbitals formed from real Slater‐type orbitals. A number of different atomic‐orbital basis sets are used. For the largest basis, a calculated energy of −15.8478 hartree at an equilibrium Be–H bond distance of 2.52 bohr is obtained with an optimized 80‐term wavefunction. Based on previous estimates of the Hartree‐Fock energy and the present results, this figure represents approximately 55% of the total correlation energy of the molecule, which is estimated to be −0.140 hartree. Using potential curves obtained from this wavefunction, the fundamental symmetric and asymmetric vibration frequencies are calculated to be 2083 and 2497 cm−1, respectively. The related force constants are also given. There are no experimental data available for comparison. The computed wavefunctions are discussed and comparisons made with elementary valence bond functions.