convergence



Dear CCLers,
 I would like to perform an optimization of inhibitor in the active site
 of the enzyme, using ONIOM in Gaussian98. Some of the enzyme active site
 fragments are frozen, while others as well as inhibitor are free to
 move. However, there is a problem with convergence in third step of the
 optimization. This is a fragment from the output file:
 ------------
 GradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGradGrad
  Berny optimization.
  Use GDIIS/GDPIS optimizer.
  Internal  Forces:  Max     0.122271245 RMS     0.022900677
  Search for a local minimum.
  Step number   3 out of a maximum of 390
  All quantities printed in internal units (Hartrees-Bohrs-Radians)
  Swaping is turned off.
    2   1 -0.2994080E-01  0.1587312      0.1886258
  Update second derivatives using information from points  2  3
  Trust test= 3.55D+00 RLast= 2.67D+00 DXMaxT set to 6.00D-01
  RFO step:  Lambda= 3.07895529D-02.
  Cosine:  0.361 <  0.866
  Cut down GDIIS temporarily because of the cosine check. E 7
  Maximum step size (   0.600) exceeded in Quadratic search.
     -- Step size scaled by   0.923
  SLEqS1 Cycle:  1951 Max:0.182663E-01 RMS:0.288751E-02 Conv:0.830925E-06
  SLEqS1 Cycle:  1951 Max:0.547130     RMS:0.725821E-01 Conv:0.830925E-06
  Iteration  1 RMS(Cart)=  0.07678248 RMS(Int)=  0.04090075
  SLEqS1 Cycle:  1951 Max:0.309281     RMS:0.644244E-01 Conv:0.348998E-06
  SLEqS1 Cycle:  1951 Max:0.103404     RMS:0.178235E-01 Conv:0.348998E-06
  Iteration  2 RMS(Cart)=  0.03887554 RMS(Int)=  0.01798566
  SLEqS1 Cycle:  1951 Max:0.210165     RMS:0.233334E-01 Conv:0.229509E-06
  SLEqS1 Cycle:  1951 Max:0.573045     RMS:0.728841E-01 Conv:0.229509E-06
 .
 .
 .
 .
 .
 (the lattest iteration)
 Iteration 99 RMS(Cart)=  0.04352782 RMS(Int)=  3.41598486
  SLEqS1 Cycle:  1951 Max:0.400389E-02 RMS:0.688668E-03 Conv:0.200000E-06
  SLEqS1 Cycle:  1951 Max:0.145725E-01 RMS:0.184286E-02 Conv:0.200000E-06
  Iteration100 RMS(Cart)=  0.02664367 RMS(Int)=  3.39771394
  Curvilinear step not converged.
  Error imposing constraints
  Error termination via Lnk1e in /d2/PROGRAMY/g98/l103.exe.
 --------------------
 How to resolve this problem?
 Jola Grembecka
 Institute of Organic Chemistry, Biochemistry and Biotechnology
 Wroclaw University of Technology