[molpro-user] VSCF calculation

[Fabian Berger]

Dear molpro user,
I have calculated the attached VSCF calculation. This calculations 
finished properly but the results are quite suspicious.
Please have a look at the frequencies (which are printed after the full 
VSCF calculation) below:

  Mode    Harmonic    Diagonal      VSCF      E(abs)
   21     3895.46    35100.93    94654.42   *********
   20     2287.49    11388.67     9714.29   *********
   19     2263.76     2242.11     3415.39   *********
   18     1952.70     2036.93     2797.70   *********
   17     1930.40     8892.65    13269.76   *********
   16     1041.72      582.15      257.85   *********
   15      990.83      620.67     1839.88   *********
   14      937.69      747.23     1553.29   *********
   13      894.56       88.28    12701.39   *********
   ...

While the harmonic frequencies appear to be reasonable, the 1D 
frequencies (Diagonal) and VSCF frequencies deviate significantly. 
Interestingly, the frequencies which are printed during the PES 
calculation (after the 1D part) seem to be much more similar to the 
harmonic values:

    Mode     Harmonic     Diagonal     Intens
   21 A       3895.46      3726.10     167.28
   20 A       2287.49      2214.86     149.16
   19 A       2263.76      2191.54     158.09
   18 A       1952.70      1895.77     246.07
   17 A       1930.40      1874.12     287.72
   16 A       1041.72      1035.21     342.11
   15 A        990.83       985.04     122.05
   14 A        937.69       949.79      39.75
   13 A        894.56       933.24     426.63
   ...

I have the following questions:

1) What is the difference between the 1D frequencies after calculating 
the 1D potentials and the full PES calculation?
2) Why do such non-senseful frequencies arise after the calculation of 
the coupling terms in the 1D frequencies?
3) Which input parameters could I adjust to fix this problem?

Thank you very much!

Best regards,
Fabian Berger


Input file:

  ***,anharm
  memory,960,m
  file,1,surfdebug.int
  file,2,surfdebug.wf
  angstrom
geometry={
    O,     1.37395990000000,    3.12849230000000,    -2.72838240000000
    Al,     0.11308370000000,    1.80597310000000,    -3.67800270000000
    O,     -1.01719110000000,    2.68772110000000,    -2.58192110000000
    Si,     0.01089600000000,    3.62802360000000,    -1.76857130000000
    H,     2.24328820000000,    2.96029440000000,    -2.35571480000000
    H,     0.59049360000000,    0.37640650000000,    -3.19723810000000
    H,     0.05245040000000,    2.19748800000000,    -5.20403290000000
    H,     -0.17319630000000,    5.08032320000000,    -1.91244630000000
    H,     0.29860050000000,    3.28203280000000,    -0.36344240000000
}

! structure relaxation
  basis,default=cc-pvtz
  {hf
  accu,14}
  ccsd(t)
  optg

  ! hessian
  mass,iso
  frequencies,symm=no

  ! PES calculation
  label1
  int
  {hf
  start,atden
  accu,14}
  ccsd(t)
  goto,label3

  label2
{df-rks,pbe0;disp}
goto,label3

  label3
  {surf,start1D=label1,sym=no,ndim=2,ngrid=8,plot=2
  vmult,start2D=label2,Multi=1
  disk,save=5600.2,where=home,dump='surfdebug.pot'}

  ! VSCF
  poly,dipole=0
  vscf,type=poly,thermo=1,dipole=0