Potential curve for linear symmetric H₃

The configuration interaction (CI) method is applied to calculate the potential curve for linear symmetric H3. The configurations are constructed from pseudo‐natural orbitals in order to improve the convergence of the CI expansion. The computed barrier energy is 10.1 kcal. This is an upper bound and has a probable error of 0.5 kcal. The method used in this calculation is critically evaluated and specifications of a projected calculation to reduce the error to less than 0.2 kcal are given. Copyright © 1971 John Wiley & Sons, Inc.