[molpro-user] how to handle singlet diradical?

[MHT]

I met the same problem as following, please see "OCC"
"The total number of orbitals must be equal to (elec+spin)/2"
does this still work for singlet diradical: _up_, _down_,
Thanks!

    * To: molpro-user at xxxxxxxxxx
    * Subject: [molpro-user] singlet diradical
    * From: ghoffman <ghoffman at xxxxxxxxxxxx>
    * Date: Mon, 13 Jun 2005 10:14:09 -0400
    * Sender: owner-molpro-user at xxxxxxxxxxxxxxxxxxxx

Hello,

I need some helpful advice for performing a clculation on a singlet 
diradical.  This is a triatomic species with 16 electrons and Cv symmetry.  
The two unpaired electrons are in orbitals of different symmetry 
(1=totally symmetric and 2=antisymmetric with respect to reflection in the 
symmetry plane).  Therefore, the symmetry of the electronic state is 2.  
Because this is a singlet state then, the command for the Hartree-Fock 
calculation ought to be:

uhf;wf,16,2,0;occ,7,2;open,7.1,-2.2;

The negative sign, according to the manual, designates that the spins of 
the two unpaired electrons are opposed.  However, with this input (and 
just about every other one I could think of), the following error message 
is returned when the calculation crashes:

 SYMMETRIES FROM ORBITAL RESTRICTIONS AND WF CARD NOT CONSISTENT:   2   2  
MS2= 0  NOPEN= 2

 ERROR EXIT
 CURRENT STACK:      MAIN

Surely, somebody out there has performed calculations on singlet 
diradicals.  How does one get Molpro to understand the desired electron 
configuration?

Thanks in advance.

Gerry Hoffman



Gerald J. Hoffman
Assistant Professor of Chemistry
Edinboro University of Pennsylvania
Edinboro, PA 16412

814-732-2813

ghoffman at xxxxxxxxxxxx