[molpro-user] how to handle singlet diradical?

[MHT]

Hi, thank you for reply and I really, really appreciate it!
I am not familiar with diradical calculation and it's my first 
time, accurately. I am doing some repeating-work. It's only test and 
practice on reference JPCA,109,7489-7499,2005.

"The diradical are species with a pair of degenerate molecular orbitals 
and two electron." You may easyly find this definition by goole since it's 
first result.

In the reference, a triplet birdical *ABCD*, could be optged;
But the singlet biradical/diradical couldn't. 

Q1: biradical==diradical ?
   (English is not my mother language.)

Q2: what's singlet diradical? Do the two electron locate on same atom? on 
two orbitals? on one of the pair of degerate orbitals? or else? 
Like, **ABCE, or *ABCD* (letf * spin up, the right * spin down)

Q3: when I repeat the reference's sinlet diradical geom just via 
multi;occ,16;closed,8;wf,24,1,0;, I got the following orbital, it's 
not sound reasonable. What should I do? Thanks again!

 Molecular orbitals read from record     2140.2  Type=MCSCF/NATURAL (state 
1.1)
 Occupation numbers read from record     2140.2  Type=MCSCF/NATURAL (state 
1.1)
 Orbital energies read from record       2140.2  Type=MCSCF/NATURAL (state 
1.1)
 Redundancy group numbers read from rec  2140.2  Type=MCSCF/NATURAL (state 
1.1)

 DUMP ORBITAL  1.1 AS ORBITAL    1  occ=    2.0000  eig=  -20.5886  GROUP=   
2
 DUMP ORBITAL  2.1 AS ORBITAL    2  occ=    2.0000  eig=  -11.2879  GROUP=   
2
 DUMP ORBITAL  3.1 AS ORBITAL    3  occ=    2.0000  eig=  -11.2376  GROUP=   
2
 DUMP ORBITAL  4.1 AS ORBITAL    4  occ=    2.0000  eig=   -1.1611  GROUP=   
2
 DUMP ORBITAL  5.1 AS ORBITAL    5  occ=    2.0000  eig=   -0.9770  GROUP=   
2
 DUMP ORBITAL  6.1 AS ORBITAL    6  occ=    2.0000  eig=   -0.7683  GROUP=   
2
 DUMP ORBITAL  7.1 AS ORBITAL    7  occ=    2.0000  eig=   -0.5973  GROUP=   
2
 DUMP ORBITAL  8.1 AS ORBITAL    8  occ=    2.0000  eig=   -0.5550  GROUP=   
2
 DUMP ORBITAL  9.1 AS ORBITAL    9  occ=    1.9842  eig=   -0.4991  GROUP=   
3
 DUMP ORBITAL 10.1 AS ORBITAL   10  occ=    1.9791  eig=   -0.6989  GROUP=   
3
 DUMP ORBITAL 11.1 AS ORBITAL   11  occ=    1.9710  eig=   -0.7112  GROUP=   
3
 DUMP ORBITAL 12.1 AS ORBITAL   12  occ=    1.3044  eig=   -0.2158  GROUP=   
3
 DUMP ORBITAL 13.1 AS ORBITAL   13  occ=    0.6978  eig=   -0.0936  GROUP=   
3
 DUMP ORBITAL 14.1 AS ORBITAL   14  occ=    0.0285  eig=    0.7385  GROUP=   
3
 DUMP ORBITAL 15.1 AS ORBITAL   15  occ=    0.0196  eig=    0.6612  GROUP=   
3
 DUMP ORBITAL 16.1 AS ORBITAL   16  occ=    0.0152  eig=    1.0523  GROUP=   
3
 Frequency information read from record  5400.2


On Sat, 22 Apr 2006, H. -J. Werner wrote:

> It is not possible to to open-shell singlets with rhf or uhf.
> Only high-spin states (single Slater determinants) are possible.
> Use mcscf for open-shell singlets!
> Joachim Werner
> On Sa, 22 Apr 2006, MHT wrote:
> 
> >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
> >
> >
> >
> >
> 
> 

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