Forbidden Ions in Field Evaporation

The inclusion of quadratic field terms in the usual Muller-type expression for predicting zero-Q evaporation field for a chemical element yields a fourth-order equation. This will be called here the "type A" approach, and is similar to the mathematics of the simple-image-hump model. An alternative approach is the inclusion of the quadratic field terms that yields a second-order equation. This will be called here the "type B" approach and is similar to the mathematics of the change-exchange models. The "type B" theories are in principle better models of field evaporation than :type A" theories, and that the use of "type A" theories in field evaporation should be abandoned