Dear Ajimala,

You mean to run a reaction coordinate method for a certain bond or distance. For an example, If you have A----B distance of 4 A, you should decrease the distance in increment of 0.1 A for 28 cycles until reaching a distance of 1.2 A. This will give you the energy values versus A---B distance (IRC, potential energy profile).

Generally this calculations are done to locate transition state or scanning the change in energy versus distance.

You can use DFT, ab initio (different bases sets) or semi-empirical methods installed in Gaussian 09.

For more on this topic, please use the following link:

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

Hoping this will be helpful,

Rafik

 Dear Ajmala,

Follow the steps as:

1. Display the gaussian visualizer

2. in edit toolbar, select redundant coordinates

3. click on add

4. click on unidentified drop down, and select bond (or angle etc. wahtever you want to do?)

5. select the bond which you want to scan in the visualized directly or type the atom numbers in the coordinate boxes.

6. in the add drop down select scan coordinate

then give no. of steps and the step size.. CAUTION: For example if you want to scan a bond between A and B, if the initial distance between the two atoms is 2 angstroms, and you want it to scan upto 1 angstrom that means you have to decrease the distance by 1 angstrom (2-1), if you selsct a step[ size of 0.1 angstrom, then in total you have to give 10 steps. but size of step will be -0.1 because you have to decrease the distance from 2 to 1, and in case you want to increase the disatnce from suppose 2 to 3 angstroms  the n you have to give ten steps and step size to be selected is +0.1( because you are increasing the bond length here)

7. press ok, otherwise the seeting will have no effect.

It will help.. if you still find any dificulty, feel free to ask......WISH U GOOD LUCK....

With regards

Haamid RasooL Bhat