From giovanni |-at-| sg2.csrsrc.mi.cnr.it  Tue Jan  7 13:14:45 1997
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Date: Tue, 7 Jan 1997 09:42:44 -0800
From: giovanni #at# sg2.csrsrc.mi.cnr.it (Giovanni Scalmani)
Message-Id: <199701071742.JAA13792:~at~:sg2.csrsrc.mi.cnr.it>
To: chemistry- at -www.ccl.net
Subject: Electrostatic_effects_in_molecular_crystals



Dear friends,

I am wondering about the following problem:

I would like to model - by means of ab-initio calculations - 
the electrostatic effects on a single molecule due to the
crystalline environment within a molecular crystal, i.e. 
I would like to perform a (possibly high level) calculation 
of a single molecule's electronic structure under the 
influence of a neighbouring molecules' charge distribution. 
An iterative procedure should be necessary to attain 
self-consistency between the ab-initio charge distribution
of the reference molecule and the neighbouring molecules' 
charge distribution, which will be in turn derived from the 
reference molecule's wavefunction.

Since I have no deep knowledge of crystallography, I will 
appreciate advises about two issues:

1) Widely speaking: Is such an approach correct? Can you 
   give me some references in the literature? If I have more
   than one molecule (or even different molecular species) 
   in the cell a similar approach on more than one molecule 
   is still feasible, but is it worth while? How should I 
   model the neighbouring molecules' charge distribution 
   (Mulliken charges, charges fitted to the molecular 
   electrostatic potential, Atom-In-Molecule-derived 
   charges, orientable atomic dipoles, ... ) ?

2) More technically: do you know a program which reads the
   crystalline structure (for example from the Cambridge
   Database) and performs all coordinates manipulation I
   will need ? In particular to obtain cartesian coordinates 
   of any specified molecule in the cell surrounded by all the
   neighbouring molecules whose centers of mass are within
   a certain radius from the reference molecule's center of
   mass ?

Thank you in advance for all suggestions,

Giovanni.

----------------------------------------------------------------------
 ^^^ | SCALMANI Giovanni                 giovanni%!at!%sg2.csrsrc.mi.cnr.it
 o o | Universita' degli Studi di Milano
  |  | Dipartimento di Chimica Fisica ed Elettrochimica
 \_/ | via C.Golgi, 19                          Phone: ++39-2-26603254
     | 20133 Milano (Italy)                     Fax  : ++39-2-70638129
----------------------------------------------------------------------