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Date: Thu, 08 Dec 2005 12:19:46 -0800
From: "Bylaska, Eric J" <Eric.Bylaska@pnl.gov>
Subject: RE: [NWCHEM] higher HOMO energy than LUMO
To: Ali Sebetci <asebetci@cankaya.edu.tr>
Cc: nwchem-users@emsl.pnl.gov
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Ali,

	What kind of functional are you using?  Having a HOMO with
higher energy than the LUMO may in fact be the lowest energy state in a
DFT calculation because of self-interaction in DFT functional.  For
instance if you calculate the C2 dimer (in the singlet Sigma^+_g state)
using a restricted LDA functional, the ground state solution has a LUMO
with a lower energy than the HOMO.  


					Eric

-----Original Message-----
From: owner-nwchem-developers@emsl.pnl.gov
[mailto:owner-nwchem-developers@emsl.pnl.gov] On Behalf Of Ali Sebetci
Sent: Thursday, December 08, 2005 2:51 AM
To: nwchem-users@emsl.pnl.gov
Subject: [NWCHEM] higher HOMO energy than LUMO

Dear NWChem users,

Sometimes, after optimization and frequency calculations in DFT model, I
am ended up with a higher HOMO energy than the LUMO energy. For instance
the following output:

 Vector   35  Occ=2.000000D+00  E=-1.960371D-01
              MO Center= -1.8D-05,  3.5D-05,  3.6D-07, r^2= 4.3D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    38      0.606863  2 Pt dxy               86     -0.606830  4 Pt dxy
    64      0.478231  3 Pt dyy               16     -0.478204  1 Pt dyy
    13      0.441050  1 Pt dxx               61     -0.440974  3 Pt dxx
    44      0.197941  2 Pt dxy               92     -0.197928  4 Pt dxy
    70      0.152698  3 Pt dyy               22     -0.152694  1 Pt dyy

 Vector   36  Occ=2.000000D+00  E=-1.921981D-01
              MO Center=  2.5D-05, -3.7D-05,  1.3D-07, r^2= 4.4D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    14      0.873936  1 Pt dxy               62      0.873923  3 Pt dxy
    86     -0.693920  4 Pt dxy               38     -0.693890  2 Pt dxy
    20      0.284152  1 Pt dxy               68      0.284129  3 Pt dxy
    92     -0.261685  4 Pt dxy               44     -0.261675  2 Pt dxy

 Vector   37  Occ=0.000000D+00  E=-1.984438D-01
              MO Center= -7.8D-05,  4.1D-06, -6.4D-07, r^2= 4.2D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    39     -0.828288  2 Pt dxz               87      0.828284  4 Pt dxz
    17     -0.809661  1 Pt dyz               65      0.809542  3 Pt dyz
    45     -0.208741  2 Pt dxz               93      0.208740  4 Pt dxz
    23     -0.203196  1 Pt dyz               71      0.203168  3 Pt dyz

Vector 36 (HOMO) energy (-0.193) is greater than the vector 37 (LUMO)
energy (-0.198).
Why does the program prefer to put the electrons in a higher energy
orbital? 
Is there an option
in NWChem to stabilize the wave function as in the case of Gaussian? How
can I correct this?

When I restart the single point calculation by swapping the vectors 37
and 36, I get the following result:

 Vector   35  Occ=2.000000D+00  E=-1.791164D-01
              MO Center= -6.2D-04, -5.2D-04,  7.6D-05, r^2= 4.6D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    90      0.493474  4 Pt dzz               42      0.493283  2 Pt dzz
    18     -0.388581  1 Pt dzz               66     -0.388183  3 Pt dzz
    85     -0.277350  4 Pt dxx               37     -0.277262  2 Pt dxx
    16      0.250045  1 Pt dyy               64      0.249749  3 Pt dyy
    88     -0.193798  4 Pt dyy               40     -0.193713  2 Pt dyy

 Vector   36  Occ=2.000000D+00  E=-1.767279D-01
              MO Center= -6.3D-04, -2.3D-04,  1.2D-04, r^2= 4.3D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    87     -0.859526  4 Pt dxz               39      0.859365  2 Pt dxz
    17      0.765946  1 Pt dyz               65     -0.765109  3 Pt dyz
    93     -0.235096  4 Pt dxz               45      0.235050  2 Pt dxz
    23      0.202455  1 Pt dyz               71     -0.202218  3 Pt dyz

 Vector   37  Occ=0.000000D+00  E=-1.983823D-01
              MO Center=  3.4D-04,  4.9D-05, -1.1D-04, r^2= 4.5D+00
   Bfn.  Coefficient  Atom+Function         Bfn.  Coefficient
Atom+Function
  ----- ------------  ---------------      ----- ------------
---------------
    62     -0.846929  3 Pt dxy               14     -0.846644  1 Pt dxy
    38      0.732718  2 Pt dxy               86      0.732668  4 Pt dxy
    44      0.266760  2 Pt dxy               68     -0.266759  3 Pt dxy
    92      0.266747  4 Pt dxy               20     -0.266711  1 Pt dxy


Thanks in advance.

Ali.