Subject: G94:freq iterations SUMMARY

From: Elmar Gerwalin <[email-masked]>
Date: Sun, 13 Jul 1997 17:42:14 +0200

(I asked : 
  How much steps including the output line
  "Re-enter D2Numr: IAtom=  1 IXYZ=2 IStep= 1."
  does a G94 calculation " B3LYP freq=(numer,restart)"
  (using Cs symmetry) perform ?
)

Thanks for all who answered !
Here's the summary (on your request)

The "opinions" cover the range from 

 3N*1 "mostly" to 7N  steps.

I can't give a correct answer now, just read the following statements 
that were sent to me.
It hasn't become clear (to me) why G94 "mostly" does 6 (or 7) steps 
for each atom, only 5 steps for atoms lying in the symmetry plane
and why my job performs 6  steps for ANY atom, although working in
Cs symmetry.
I will go on checking that out and perhaps tell you soon!

------ here's the summary ------

1.) 3N to 6N
 
  From [email-masked]  Fri Jul 11 13:49:59 1997

It's easy: N atoms, 3 cartesian coordinates each, 1 step
most of the time, 2 steps if g94 finds one is not sufficient.
Hence the number of calcs will be somewhere between
3N and 6N.

2.) 6N(+1), decreased by symmetry, 5 or 6 steps per atom

For example, in the case of CH2 molecule, Gaussian calculates 
force constants like next 10 steps.

1  The SCF and gradient calculation at the equilibrium point.
2  Re-enter D2Numr: IAtom=  1 IXYZ=1 IStep= 1.   Carbon  X axis  + direction
3  Re-enter D2Numr: IAtom=  1 IXYZ=2 IStep= 1.   Carbon  Y axis  + direction
4  Re-enter D2Numr: IAtom=  1 IXYZ=3 IStep= 1.   Carbon  Z axis  + direction
5  Re-enter D2Numr: IAtom=  1 IXYZ=3 IStep= 2.   Carbon  Z axis  - direction
6  Re-enter D2Numr: IAtom=  2 IXYZ=1 IStep= 1.   hydrogen X axis + direction
7  Re-enter D2Numr: IAtom=  2 IXYZ=2 IStep= 1.   hydrogen Y axis + direction
8  Re-enter D2Numr: IAtom=  2 IXYZ=2 IStep= 2.   hydrogen Y axis - direction
9  Re-enter D2Numr: IAtom=  2 IXYZ=3 IStep= 1.   hydrogen Z axis + direction
10 Re-enter D2Numr: IAtom=  2 IXYZ=3 IStep= 2.   hydrogen Z axis - direction

The number of steps are 6N+1, (N=number of atom). 
But, symmetry(for example C2V) can decrease the number 
to 10(from 19). The skipped 9 steps are,

1  Re-enter D2Numr: IAtom=  1 IXYZ=1 IStep= 2.   
2  Re-enter D2Numr: IAtom=  1 IXYZ=2 IStep= 2.   
3  Re-enter D2Numr: IAtom=  2 IXYZ=1 IStep= 2.   
4  Re-enter D2Numr: IAtom=  3 IXYZ=1 IStep= 1.   
5  Re-enter D2Numr: IAtom=  3 IXYZ=1 IStep= 2.   
6  Re-enter D2Numr: IAtom=  3 IXYZ=2 IStep= 1.   
7  Re-enter D2Numr: IAtom=  3 IXYZ=2 IStep= 2.   
8  Re-enter D2Numr: IAtom=  3 IXYZ=3 IStep= 1.   
9  Re-enter D2Numr: IAtom=  3 IXYZ=3 IStep= 2.   

In the case of triatomic molecule XMY(Cs symmetry) is calculated, 
the required number of steps is 16,

1  The SCF and gradient calculation at the equilibrium point.
2  Re-enter D2Numr: IAtom=  1 IXYZ=1 IStep= 1.
3  Re-enter D2Numr: IAtom=  1 IXYZ=1 IStep= 2.
4  Re-enter D2Numr: IAtom=  1 IXYZ=2 IStep= 1.
5  Re-enter D2Numr: IAtom=  1 IXYZ=2 IStep= 2.
6  Re-enter D2Numr: IAtom=  1 IXYZ=3 IStep= 1.
7  Re-enter D2Numr: IAtom=  2 IXYZ=1 IStep= 1.
8  Re-enter D2Numr: IAtom=  2 IXYZ=1 IStep= 2.
9  Re-enter D2Numr: IAtom=  2 IXYZ=2 IStep= 1.
10 Re-enter D2Numr: IAtom=  2 IXYZ=2 IStep= 2.
11 Re-enter D2Numr: IAtom=  2 IXYZ=3 IStep= 1.
12 Re-enter D2Numr: IAtom=  3 IXYZ=1 IStep= 1.
13 Re-enter D2Numr: IAtom=  3 IXYZ=1 IStep= 2.
14 Re-enter D2Numr: IAtom=  3 IXYZ=2 IStep= 1.
15 Re-enter D2Numr: IAtom=  3 IXYZ=2 IStep= 2.
16 Re-enter D2Numr: IAtom=  3 IXYZ=3 IStep= 1.

3.) 6N, decreased by symmetry, 5 steps for atoms on the
                               symmetry plane, 6 others