[molpro-user] lmp2 geometry optimisation convergence problem

[Falk Richter]

Hi,

I'm trying df-mp2 optg  for some molecules having all some valence 
angles close to 180
and  optg is jumping arround close to a presumed equilibrium geometry, 
but does not converge.
The "step size" (what is given in the "convergence line" under "next" in 
the optimization point resumee)
is lower than 0.05 but actually never falls below 0.01. If I guess 
right, it this value which must fall below 0.01
in order to get the domains frozen for all the optimization points. 
(i.e. for all  optimization points to have the same domains)
The reason why this value is always higher than 0.01 are probably the 
large changes of some torsional angles connected
to some angles close to 180 deg  (the potential in torsional direction 
is then very shallow)
and consequently the reason for nonconvergence is the changing domain 
definition at each optimization point.
If this is the case it would make sense to adjust this 0.01 trashold.

So, is there any way to adjust this treshold ?

Is this a possible interpretation of something that can happen
or is there some error from my part (see also  the input) ?

Thanks

Falk Richter


  ***,
  MEMORY,50,M
  file,2,141.wfu
  Angstrom
  noorient
  basis=avdz
  geometry={
  C;
  C,1,R2;
  C,2,R3,1,A3;
  C,1,R4,3,A4,2,D4;
  H,1,R5,3,A5,2,D5;
  C,2,R6,3,A6,1,D6;
  C,2,R7,3,A7,1,D7;
  C,3,R8,2,A8,7,D8;
  N,7,R9,6,A9,2,180.0;
  N,6,R10,7,A10,9,0.0;
  N,4,R11,5,A11,1,180.0;
  N,8,R12,2,A12,3,180.0;
   }
  R2 =   1.54457775
  R3 =   1.43601809
  A3 =      57.5707
  R4 =   1.44771117
  A4 =     121.4228
  D4 =     251.9241
  R5 =   1.10987590
  A5 =     121.3899
  D5 =     106.9102
  R6 =   1.45523163
  A6 =     120.9002
  D6 =     254.8190
  R7 =   1.45286408
  A7 =     121.3321
  D7 =     109.2881
  R8 =   1.35230000
  A8 =     147.1963
  D8 =     -78.0080
  R9 =   1.15978019
  A9 =     145.1733
  D9 =     178.3186
  R10=   1.15998441
  A10=     146.0559
  D10=      -1.3742
  R11=   1.16060342
  A11=     148.3197
  D11=     181.8337
  R12=   1.17484329
  A12=     163.3735
  D12=     180.5848

  {df-hf;
  wf,72,1,0;
  accu,16;
  }

  {df-lmp2;
  PIPEK,METHOD=3,DELETE=1}

  optg;