tetrahedral distortion - why ?


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Forum Vet
10:32:22 AM PDT - Fri, Jun 15th 2012
NWChem automatically tries to find symmetry by default. For some reason it finds Cs symmetry instead of Td in the starting configuration. Any subsequent calculations are using the Cs symmetry, and as a result it looks like the orbital ordering leads to this geometry.

Simple fix:

  geometry noautosym

Alternatively:

 geometry

    symmetry Td

    V 0.0000 0.0000 0.0000

    O 1.0140 1.0140 1.0140

  end

Both will give you the proper Td structures.

Bert



Quote:Edward.deira Jun 15th 5:05 pm
Dear all,

Maybe this is a foul input, but the same job turns out fine on the competition's software.

So, I'm optimizing otho-vanadate (VO4-3) in the gas phase with B3LYP/6-31g (I placed the input in the end of this post), and it should be a simple tetrahedral, just like ch4.

So, I got this piece of **sucessfull** output where atom 1 is V and atoms 2 to 5 are O:

      Type          Name      I     J     K     L     M      Value     Gradient
      ----------- --------  ----- ----- ----- ----- ----- ---------- ----------
    1 Stretch                  1     2                       1.88292   -0.00003
    2 Stretch                  1     3                       1.88305    0.00003
    3 Stretch                  1     4                       1.64063   -0.00001
    4 Stretch                  1     5                       1.64063   -0.00001
    5 Bend                     2     1     3                49.61591    0.00003
    6 Bend                     2     1     4               121.56546   -0.00008
    7 Bend                     2     1     5               121.56546   -0.00008
    8 Bend                     3     1     4               120.34717    0.00003
    9 Bend                     3     1     5               120.34717    0.00003
   10 Bend                     4     1     5               110.90875    0.00006


This is what my younger co-workers call "fail".

But... why ?
I keep thinking the B3LYP/6-31g could be it, but if runs fine to a fine result in other software.

Any suggestions ?
All the best,
Edward

Input:
memory total 4 gb

start vo4

geometry
     V                   0.00000270    -0.00000085     0.00000000
     O                  -0.78410613    -1.53120837     0.00000000
     O                  -1.18224797     1.24967774     0.00000000
     O                   0.98317592     0.14076473    -1.40461359
     O                   0.98317592     0.14076473     1.40461359
end

basis
* library 6-31g
end

dft
xc b3lyp
iterations 200
end

driver
maxiter 200
end

charge -3

#task scf optimize

task dft optimize