[molpro-user] Help with SLAPAF Program

[rossi at york.cuny.edu]

Dear Sasha:

Thank you so much for your quick response.

But, the constraints are not working for me.

Here is my input file.  I don't think it can get much simpler.

*** bicyclobutane - ground state
memory,128,m

FILE,2,./wfu/test_constraint.wfu,new

geomtyp=xyz
geometry={
ANGSTROM
10
Bicyclobutane
C1          6.0  -0.8464354380  -0.1961899345   0.2856934463
C2          6.0   0.8464354380   0.1961899345   0.2856934463
C3          6.0   0.1359364305   1.4453100675  -0.2977645687
C4          6.0  -0.1359364305  -1.4453100675  -0.2977645687
H1          1.0  -1.3189804253  -0.2580074160   1.2491001668
H2          1.0   1.3189804253   0.2580074160   1.2491001668
H3          1.0   0.1708354934   1.5903287379  -1.3664594314
H4          1.0  -0.1708354934  -1.5903287379  -1.3664594314
H5          1.0   0.1455613584   2.3655897131   0.2610880557
H6          1.0  -0.1455613584  -2.3655897131   0.2610880557
}

basis=sto-3g

rcc=1.50;

hf

{optg,method=slrf
! constraint,0,bond,atoms=[C1,C4],-1.,bond,atoms=[C2,C3]
! constraint,$rcc,angstrom,bond,atoms=[C1,C2]
primitive,b1,bond,atoms=[C1,C4];
}

put,molden,test_constraint.molden;
---

Here is what I am trying to do:

If one views the bicyclobutane from above, it appears as a parallelogram
with an additional bond across the diagonal.

The intent is to obtain a relaxed potential energy curve for the opening of
two bonds that are opposite each other (See a and b below.), as one
gradually stretches them.  It requires two constraints, one for a and one
for b; and they will be held fixed for each point on the curve while all
other coordinates are varied.



                           /\a                   ||
                          /  \                   ||
                          ----        --->       ------
                          \  /                        ||
                         b \/                         ||

                       bicyclobutane            butadiene


The bonds a, b are to be constrained to a series of values:
1.5,1.6,1.7,1.8,1.9,2.0 .

By the time the a and b bonds reach 2.0, then butadiene is well on its way
to being formed (incipient butadiene).

None of the constraints work.

1) Both forms of the constraint command give me an error.

2) molpro doesn't recognize the primitive command.

I have attached the output from molpro.

Please help.

Regards,

Angelo

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