An approximation technique is suggested which should prove useful for calculation of correlated electronpositron wave functions in insulating solids. This technique is based on the Born-Oppenheimer methods of calculating molecular properties, and is physically grounded in the idea that the Coulomb interaction between electrons and positron should affect the positron more profoundly than it does the tightly bound electrons. The technique is used to calculate, in the lowest order approximation, a wave function for solid argon showing the effects of correlation. This wave function is used to compute positron lifetime and angular distribution of annihilation radiation. The lifetime is found to be in reasonable agreement with experiment; on the other hand, the use of the lowest order wave function for calculation of the angular distribution gives results which are apparently in disagreement with experiment.

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