Subject: MOPAC ERROR MSG

From: [email-masked] (Dr. James Stewart)
Date: Mon, 12 Sep 94 16:20:20 PDT

Apropos
"I'm trying to run an AM1 calculation on the benzocoronene oxidation dication
(benzocoronene minus 2 electrons) in the triplet state, using MOPAC93.  My
list of keywords is AM1 PRECISE CHARGE=2 VECTORS TRIPLET, and I get the error
message "Specified spin component not spanned by active space".  Can anyone
tell me what I'm doing wrong?  I was able to get the analogous calculation
on coronene oxidation dication, using MOPAC 6 with the same keyword line,
except without the word VECTORS.  Thanks for the help.
"

In earlier MOPAC programs the key-word TRIPLET had caused some
confusion: some users thought it meant `do an SCF then do a C.I.
using the HOMO and LUMO, and select the triplet root.' Others
thought it meant `put an electron in the HOMO and an electron in
the LUMO, go SCF, then do a C.I. and select the triplet.'  To
resolve the ambiguity, I have re-defined TRIPLET so that the user
has to specify which option is wanted.

This is first mentioned on page 2 of the MOPAC 93 Manual.

To answer your question, either ass C.I.=2 or add OPEN(2,2) to
the keyword line.  This will give you the first or the second
option described above.

James J. P. Stewart