Subject: STRANGE PROBLEM WITH FREQS

From: "E. Lewars" <[email-masked]>
Date: Mon, 25 Dec 1995 14:25:18 -0500 (EST)

1995 Dec 25

MERRY CHRISTMAS AND A HAPPY 1996!

Hello, I have an interesting problem connected with Spartan. I did an opt/freq
on the unusual molecule      Me            Me
                               \          /
  Me        /C\        Me        C------ C
   \      //  \ \     /          | \   /  |
     \ /-/------\-\ /            |   C    |    C(C-Me)4   Tetramethylpyramidane
      [/__________\]             | /   \  |
     /              \            C--------C    NOTE: pyramidane, C(CH)4, is
   /                  \        /            \        a relative minimum (no
 Me                    Me    Me              Me     imaginary freqs) at the
                                                    HF/6-31G*, MP2/6-31G* and
                        C4v                         MP2/6-31++G** levels.

           (The HF/6-31G* geom is given in the file below)

 The HF/6-31G* opt proceeded normally (E=-347.628 348), but the freqs are
 absurd:
        -68748.51   E
        -68748.51   E
        -22116.22   A1
        -11996.37   B1
        (followed by sensible +ve freqs
            151.29  B2
            151.88  A2
             etc.)

         ZPE = 566.02 kcal/mol

  Finding this hard to accept, I used the Spartan HF/6-31G* geom as input for
a Gaussian 92 HF/6-31G* opt/freq.  The Gaussian opt (which needed only one
opt cycle) gave the same E as Spartan (-347.628 348 6) but the freqs and ZPE
were quite different (the E from the freq job was also -347.628 348):

             +163.42  E
             +163.42  E
             +164.03  A2
             +164.64  B1
             +182.69  B2
                etc

            ZPE = 120.42 kcal/mol

  Has anyone any idea why the two programs gave such different results?
I presume that the "huge negative" freqs are simply wrong, and the Gaussian
freqs are correct; the parent compound C5H4, and other substituted pyramidanes,
gave normal freqs.

  Thanks for any suggestions.

 Errol Lewars

--------------------------
This is the Spartan HF/6-31G* geom (=G92 HF/6-31G* geom) and connectivity:

C OPT HF DIRECT 6-31G* DAMP=.75 HESS=ARCH GUESS=READ 
FREQ maxcycle=200
Input:  C4v 3-21G
0 1
;6   2.504069003   0.000000000   0.057343366
 6   0.000000000   1.017992876   0.196489929
 6   1.017992876   0.000000000   0.196489929
 6  -1.017992876   0.000000000   0.196489929
 6   0.000000000  -1.017992876   0.196489929
 6   0.000000000   0.000000000  -1.055200740
 6   0.000000000  -2.504069003   0.057343366
 6   0.000000000   2.504069003   0.057343366
 6  -2.504069003   0.000000000   0.057343366
 1   0.000000000  -2.982679331   1.031452811
 1   0.876613239  -2.837789716  -0.485825815
 1  -0.876613239  -2.837789716  -0.485825815
 1  -2.837789716  -0.876613239  -0.485825815
 1  -2.837789716   0.876613239  -0.485825815
 1  -2.982679331   0.000000000   1.031452811
 1   0.876613239   2.837789716  -0.485825815
 1   0.000000000   2.982679331   1.031452811
 1  -0.876613239   2.837789716  -0.485825815
 1   2.982679331   0.000000000   1.031452811
 1   2.837789716   0.876613239  -0.485825815
 1   2.837789716  -0.876613239  -0.485825815
ENDCART
FROZEN
ENDFROZEN
PI
ENDPI
PAIRING
ENDPAIR
HESSIAN
    1    1    1    1    1    1    1    1    1   13   13   13
   13   13   13   13   13   13   13   13   13
    6    2    1
    2    8    1
    2    3    1
    2    4    1
    3    1    1
    3    6    1
    3    5    1
    4    9    1
    6    4    1
    4    5    1
    6    5    1
    5    7    1
    7   10    1
    7   11    1
    7   12    1
    9   13    1
    9   14    1
    9   15    1
    8   16    1
    8   17    1
    8   18    1
    1   19    1
    1   20    1
    1   21    1
ENDHESS