Subject: "sparkles" in MOPAC

From: [email-masked] (makula-bisance)
Date: Wed, 21 Sep 1994 17:04:39 +0200 (MET DST)

Dear Netters,

I would like to calculate with MOPAC the geometry of an organic anion.
I am not sure that the calculation of an ion alone in the gas-phase 
would be very realistic (mainly because of intramolecular electrostatic
repulsion), so I tried to use the so-called "sparkles" which are defined in
the MOPAC manual as "pure ionic charges" or more precisely as an "integer
charge at the center of a repulsion sphere of form exp(-alpha*r)".
The manual explains further that the sparkles can be used as counterions.

Unfortunately, my MOPAC calculation with a positive sparkle "+" ended up
with the positive charge almost superimposed on the atom of my anion bearing
most of the negative charge.

Have I missed something in the keyword specification ? does anybody have
experienced this MOPAC feature with some success ? (some refs would be 
welcome ).

I will summarize the answers for the net.
Please use the following e-mail address (not the one in the From: line)
if you want to answer directly to me:

[email-masked]

Dr Remi Le Goas
Computer Aided Molecular Design
Rhone-Poulenc Agrochimie
Lyon - FRANCE