Subject: Anisotropic Hyperfine Constants

From: <[email-masked]>
Date: Wed, 26 Mar 1997 22:15:43 +1100

Dear Netters,

I recently asked a question of you regarding the theoretical
determination of the nuclear magnetic dipolar-electronic magnetic
dipolar anisotropic hyperfine coupling constants.  I thank everybody
for there responses.  I was about to post a summary of everyone's
responses as well as my own summary, but decided to hold off until I
could get the following point cleared up which has been nagging me for
the past week or so.

I've been able to verify that the hyperfine constants, A_ab, are, in
fact, proportional to the expectation values of the electric field
gradient, _averaged_over_spin_density_, rather than charge density as
is the case for the actual electric field gradient, ONLY for A_zz,
A_zx and A_zy.

In the case of A_xx, A_yy and A_xy the electronic spin operator
appearing in the hyperfine Hamiltonian is _only_ s_x or s_y, i.e., s_z
does not appear for these terms, yet the same "averaged over spin
density" expressions are used to calculate these constants as well.
My question is, how is this possible, i.e., why does it seem that s_z
was substituted for s_x and s_y?

Thanks in advance,

Fiona Bettens.