Dear mate

Freezing coordinates during a IRC calculation is not as straightforward as in other type of calculations because modredundant keyword crashes. There is however another keyword that can by-pass this problem, the ReadOptimize, which tells the program which atoms are going to be optimized. Let me show you an example of how an input with this keyword should be:

# irc=(calcall,readoptimize) hf/sto-3g

/blank line

Title Card Required

/blank line

-1 1

H -0.59043200 -0.60055000 0.92879100

H -0.59043200 -0.60056400 -0.92876900

Cl -2.81664800 -0.42956000 -0.00000100

C -0.69758700 -0.05802200 0.00000700

Br 1.73358500 -0.16003500 -0.00000100

C -0.81242500 1.48292200 -0.00000100

H -1.36002900 1.80500200 0.88001700

H 0.16834500 1.94545000 0.00009600

H -1.35985800 1.80500600 -0.88012200

/blank line

notatoms=C

/blank line

It is a IRC calculation starting from the TS of the SN2 reaction between chloroethane and bromine (run the calculation and see what happens with the carbons). Imagine that I want to freeze all carbons. Then I use the keyword through irc=readoptimize, and after the geometry section I tell the program which atoms I want or don't want to optimize. notatoms=C means "Optimize all non-carbon atoms".

There are several combinations to specify which atoms you want to optimize. In your case, as you are dealing with a catalyst, you can use the next syntaxis (imagine that your whole structure has 200 atoms, atoms 1-50 are the reagents and 51-200 the catalyst)

noatoms atoms=1-50

"noatoms" empties the list of atoms that are being optimized, then "atoms=1-50" adds those atoms to the list. As you didn't specify anything for atoms 51-200 after the "noatoms" keyword, the will NOT be optimized. Other option will be:

notatoms=51-200

Just keeping those atoms away from the optimization. Obviously you need to sort the input, but that is an easy job. Take a look on http://www.gaussian.com/g_tech/g_ur/k_opt.htm and see the options of ReadOptimize

Hope you find it helpful

Dear mate

Freezing coordinates during a IRC calculation is not as straightforward as in other type of calculations because modredundant keyword crashes. There is however another keyword that can by-pass this problem, the ReadOptimize, which tells the program which atoms are going to be optimized. Let me show you an example of how an input with this keyword should be:

# irc=(calcall,readoptimize) hf/sto-3g

/blank line

Title Card Required

/blank line

-1 1

H -0.59043200 -0.60055000 0.92879100

H -0.59043200 -0.60056400 -0.92876900

Cl -2.81664800 -0.42956000 -0.00000100

C -0.69758700 -0.05802200 0.00000700

Br 1.73358500 -0.16003500 -0.00000100

C -0.81242500 1.48292200 -0.00000100

H -1.36002900 1.80500200 0.88001700

H 0.16834500 1.94545000 0.00009600

H -1.35985800 1.80500600 -0.88012200

/blank line

notatoms=C

/blank line

It is a IRC calculation starting from the TS of the SN2 reaction between chloroethane and bromine (run the calculation and see what happens with the carbons). Imagine that I want to freeze all carbons. Then I use the keyword through irc=readoptimize, and after the geometry section I tell the program which atoms I want or don't want to optimize. notatoms=C means "Optimize all non-carbon atoms".

There are several combinations to specify which atoms you want to optimize. In your case, as you are dealing with a catalyst, you can use the next syntaxis (imagine that your whole structure has 200 atoms, atoms 1-50 are the reagents and 51-200 the catalyst)

noatoms atoms=1-50

"noatoms" empties the list of atoms that are being optimized, then "atoms=1-50" adds those atoms to the list. As you didn't specify anything for atoms 51-200 after the "noatoms" keyword, the will NOT be optimized. Other option will be:

notatoms=51-200

Just keeping those atoms away from the optimization. Obviously you need to sort the input, but that is an easy job. Take a look on http://www.gaussian.com/g_tech/g_ur/k_opt.htm and see the options of ReadOptimize

Hope you find it helpful

Mr./Mrs/Miss Chadaram,

You canpay attention to the following link as well as:

http://www.gaussian.com/g_tech/g_ur/k_irc.htm