NMR Shielding Isosurfaces

[Betty <lori #*at*# victory.scs.uiuc.edu>]

 Greetings!
 I am investigating the NMR chemical shielding tensors in various amino
 acid residues and peptides using primarily deMon and Gaussian.  I would
 like to include graphical interpretations of the chemical shielding in my
 analysis but have been unsuccessful in finding a satisfactory description
 of chemical shielding isosurfaces.
 The Gaussian website shows examples of such isosurfaces and provides a
 tutorial to generate the isosurfaces but do not actually give an
 explanation of "...the shielding density applied in the z-direction
 mapped on the current density iso-surface in the z-direction..."
 I am currently awaiting a response from Gaussian to this question but
 thought a CCL subscriber may be able to provide some insight.  I apologize
 if this is not the proper forum for this question but would greatly
 appreciate any comments.
 Many thanks!
 Lori Sanders
 Graduate Assistant
 University of Illinois
 Urbana IL 61801