From: [email-masked] (Ms. Chitra)
Date: Sat, 27 Apr 1996 23:36:21 +0600

Dear CCL members,

    My problem is the following:

    Just as you have normal modes defined in the solid phase, you can
define a set of instantaneous normal modes for a non-rigid fluid-like
phase. Basically, if you have a set of N atoms in this fluid, you can
write out a ( 3N x 3N )mass-weighted Hessian matrix, whose eigen values 
yield the force constants corresponding to the instantaneous normal 
modes. The Hessian matrix elements are defined as the second derivatives 
of the potential wrt the coordinates.

    Now, suppose this fluid-like phase is enclosed in a container
with whose walls it interacts.  The container itself is kept rigid.
The potential, in this case, will be a sum of two terms:  one due to
interactions amongst the fluid particles and another corresponding to
interactions between the fluid and the wall. (Let us assume that there
are N atoms in the fluid and there are NW wall atoms).
Could anyone of you tell me the kind of Hessian matrix that is involved
in this case?  Any reply will be appreciated.

    Please address the replies to me at [email-masked].  I 
will summarize to the list.

    Thank you for your time,

    Chitra.

 ([email-masked])