Molecular Orbital Study of Be4

An LCAO MO SCF study was made of the square, planar ${\mathrm{Be}}_4$ complex. A complete SCF calculation was performed at four different internuclear distances. In this series of calculations all one‐ and two‐center integrals were evaluated exactly and the value of each three‐ and four‐center integral was estimated by a method considered most suitable for it. The results showed the complex unstable. The energy values when extrapolated to infinite internuclear distance were in good agreement with experiment. A second series of calculations was made to determine the effect of three‐ and four‐center integral approximations on the energies. Here all the multicenter integrals were evaluated by one type of approximation. This introduced a relatively small change in the integral values, but large changes in the energies. The study emphasizes the need for exact values of three‐ and four‐center integrals before exact calculations can be undertaken.