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It is well known that molecular orbital wavefunctions do not give quantitatively meaningful potential energy surfaces. Much attention has previously been directed towards the failure of molecular orbital theories to predict the correct energy dependence for changes in bond lengths. In this paper dependence of the correlation energy upon bond angle is considered. Direct calculation of the total correlation energy for a polyatomic molecule is a formidable undertaking and has not been achieved even for the simplest polyatomic molecules. We investigate in this repot that part of the correlation energy which may be obtained from the interaction of low-lying electronic configurations. Some qualitative aspects of the problem are discussed using Walsh and Mulliken diagrams of molecular orbital energies as a function of angle. Results of calculations on $BeH2,NO2+$ and $O3$ are reported. The possibility of double minima in the potential surfaces for $AB2$ type molecules is considered.