Problems with Maximum Overlap Model (MOM)

[Ivan Infante]

Hi, 

  I am trying to use MOM and I have some problems.
I start from a ground state closed-shell converged wavefunction, and I use 
the restart file for the MOM calculation. I just de-occupy the beta HOMO to 
occupy the LUMO beta. 
The HOMO-LUMO gap of this system is around 2.0 eV, so there shouldnt be any 
problem to converge the excited state. 
However, after a few iterations, when the DIIS kicks in, it immediately 
swaps to the ground state energy (E = -5725.1289....) .

  Step     Update method      Time    Convergence         Total energy    
Change

  
------------------------------------------------------------------------------

     1 P_Mix/Diag. 0.40E+00   13.8     0.32547826     -5724.9981579203 
-5.72E+03

     2 P_Mix/Diag. 0.40E+00   16.1     0.18145011     -5725.0429211687 
-4.48E-02

     3 P_Mix/Diag. 0.40E+00   16.0     0.11353690     -5725.0753406595 
-3.24E-02

     4 P_Mix/Diag. 0.40E+00   16.1     0.06733805     -5725.0961299910 
-2.08E-02

     5 DIIS/Diag.  0.20E-02   16.1     0.04123847     -5725.1090261343 
-1.29E-02

     6 DIIS/Diag.  0.11E-02   16.1     0.00192988     -5725.1289018949 
-1.99E-02

     7 DIIS/Diag.  0.31E-03   16.1     0.00128342     -5725.1289258147 
-2.39E-05

     8 DIIS/Diag.  0.28E-03   16.1     0.00032442     -5725.1289261285 
-3.14E-07

     9 DIIS/Diag.  0.96E-04   16.1     0.00018951     -5725.1289310034 
-4.87E-06

    10 DIIS/Diag.  0.45E-04   16.1     0.00004841     -5725.1289312796 
-2.76E-07

    11 DIIS/Diag.  0.17E-04   16.1     0.00003119     -5725.1289314498 
-1.70E-07

    12 DIIS/Diag.  0.11E-04   16.1     0.00001487     -5725.1289314674 
-1.76E-08

    13 DIIS/Diag.  0.28E-05   16.1     0.00000367     -5725.1289314718 
-4.34E-09


  *** SCF run converged in    13 steps ***

I tried to play with the alpha mixing parameter, with a EPS_DIIS tight (to 
avoid that the DIIS interfere) but no success:

     1 P_Mix/Diag. 0.10E-03   13.8     0.32547826     -5724.9981579203 
-5.72E+03

     2 P_Mix/Diag. 0.10E-03   16.1     0.32544318     -5724.9981819920 
-2.41E-05

     3 P_Mix/Diag. 0.10E-03   16.1     0.32540810     -5724.9982060548 
-2.41E-05

     4 P_Mix/Diag. 0.10E-03   16.1     0.32537302     -5724.9982301087 
-2.41E-05

     5 P_Mix/Diag. 0.10E-03   16.1     0.32533795     -5724.9982541538 
-2.40E-05

     6 P_Mix/Diag. 0.10E-03   16.1     0.32530289     -5724.9982781901 
-2.40E-05

     7 P_Mix/Diag. 0.10E-03   16.1     0.32526782     -5724.9983022175 
-2.40E-05

     8 P_Mix/Diag. 0.10E-03   16.1     0.32523276     -5724.9983262361 
-2.40E-05

     9 P_Mix/Diag. 0.10E-03   16.1     0.32519771     -5724.9983502459 
-2.40E-05

    10 P_Mix/Diag. 0.10E-03   16.1     0.32516265     -5724.9983742469 
-2.40E-05

    11 P_Mix/Diag. 0.10E-03   16.1     0.32512760     -5724.9983982391 
-2.40E-05

    12 P_Mix/Diag. 0.10E-03   16.1     0.32509256     -5724.9984222225 
-2.40E-05

    13 P_Mix/Diag. 0.10E-03   16.1     0.32505752     -5724.9984461970 
-2.40E-05

    14 P_Mix/Diag. 0.10E-03   16.1     0.32502248     -5724.9984701628 
-2.40E-05

    15 P_Mix/Diag. 0.10E-03   16.1     0.32498745     -5724.9984941198 
-2.40E-05

    16 P_Mix/Diag. 0.10E-03   16.1     0.32495242     -5724.9985180680 
-2.39E-05
 
 Here it seems that is converging, but the EPS_SCF remains very high. 
When I use intermediete values of ALPHA, like 0.1 or 0.05, the calculation 
goes slow, but tends still to converge to the ground state. 

Is there something that I can use to converge my calculation to the excited 
state ? 

Thanks, 
Ivan



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