E-MAP IMPROVEMENT IN DIRECT PROCEDURES

The quality of an E map is usually affected by systematic and/or random phase errors, by amplitude truncation effects in the series representation of the electron density, by the experimental uncertainty in the estimation of \E\ and by the intrinsic nature of the Fourier coefficients used (i.e. the E's). It is shown that simple supplemental calculations can improve the quality of an E map. Large molecular fragments can often be localized in the new map even when the original one is not easily interpretable.