There are following way to Scan dihedral angle using Gaussian.

1. Relaxed Scan (OPT=Z-matrix, OPT=modredundant)

2. Rigid Scan (scan keyword)

A relaxed scan can be done with symbolic Z-matrix (internal coordinates) by using opt=Z-matrix keyword, for instance:

(in following examples D1 180.0 S 18 10 representing dihedral scan from fixed value 180.0 with stepsize of 10 degree in 18 steps, e.g., 180, 190, 200, ...., 360)

# hf/3-21g opt=z-matrix geom=connectivity

Relaxed scan (Internals)

0 1

C

O 1 B1

H 1 B2 2 A1

H 1 B3 2 A2 3 D1 0

B1 1.22731700

B2 1.11045737

B3 1.11045737

A1 122.22491841

A2 122.22491841

D1 180.00000000 S 18 10

1 2 2.0 3 1.0 4 1.0

2

3

4

A rigid scan can only be done with a symbolic Z-matrix. If you want to scan an internal coordinate, you would need to give the input in Z-matrix internal coordinates, for instance:

# hf/3-21g scan geom=connectivity

Rigid Scan (Internals)

0 1

C

O 1 B1

H 1 B2 2 A1

H 1 B3 2 A2 3 D1 0

B1 1.22731700

B2 1.11045737

B3 1.11045737

A1 122.22491841

A2 122.22491841

D1 180.00000000 S 18 10

1 2 2.0 3 1.0 4 1.0

2

3

4

GOOD LUCK

If there any problem let me know.....

look under the "scan" and "opt" keywords in the manual - it's easy!

To be honest, gaussian 03 ist not the fastes program for doing stuff like that, try ORCA they have an example for that case in the manual.

http://www.thch.uni-bonn.de/tc/orca/

It's freeware, just try it.

There are following way to Scan dihedral angle using Gaussian.

1. Relaxed Scan (OPT=Z-matrix, OPT=modredundant)

2. Rigid Scan (scan keyword)

A relaxed scan can be done with symbolic Z-matrix (internal coordinates) by using opt=Z-matrix keyword, for instance:

(in following examples D1 180.0 S 18 10 representing dihedral scan from fixed value 180.0 with stepsize of 10 degree in 18 steps, e.g., 180, 190, 200, ...., 360)

# hf/3-21g opt=z-matrix geom=connectivity

Relaxed scan (Internals)

0 1

C

O 1 B1

H 1 B2 2 A1

H 1 B3 2 A2 3 D1 0

B1 1.22731700

B2 1.11045737

B3 1.11045737

A1 122.22491841

A2 122.22491841

D1 180.00000000 S 18 10

1 2 2.0 3 1.0 4 1.0

2

3

4

A rigid scan can only be done with a symbolic Z-matrix. If you want to scan an internal coordinate, you would need to give the input in Z-matrix internal coordinates, for instance:

# hf/3-21g scan geom=connectivity

Rigid Scan (Internals)

0 1

C

O 1 B1

H 1 B2 2 A1

H 1 B3 2 A2 3 D1 0

B1 1.22731700

B2 1.11045737

B3 1.11045737

A1 122.22491841

A2 122.22491841

D1 180.00000000 S 18 10

1 2 2.0 3 1.0 4 1.0

2

3

4

GOOD LUCK

If there any problem let me know.....

Try these links

http://joaquinbarroso.com/2010/04/19/pesscan/

http://www.cup.uni-muenchen.de/ch/compchem/geom/scan.html

http://home.btconnect.com/reoakes/tips.html

There is two ways for scanning the dihedral angle.

1. Fixing all other geometrical parameters, then by writing scan. The in geometries select the dihedral angle that you want to scan. for example

D5 0.0 24 15.0

which means you start the scanning of D5 from 0.0 degree in 24 steps by 15.0 degrees in each step. You should be carefully check that other parameters are not dependent to the position of the atom which is subject to changing.

Second way is scanning the dihedral angle in steps but all other parameters are subject to full optimization. This is done by selecting OPT=MODREDUDANT and putting the following order a line after the geometries.

* 4 5 * R

9 4 5 12 S 24 15.0

the first line orders that all dihedral angles passing through 4 5 bond are subject to change with the dihedral angle 9 4 5 12 which will be scaned by 15.0 degrees in 24 steps.

I have a query, I need to scan the distance between cyclodextrin and another guest molecule. How can I do that?

I want to get the data of the scan, i need to calculate the energy and HOMO to plot curves by varing the angles

I did the scan but the out files is not enough .

the curve was given by gaussian but is not what I am looking for.

Thank you for your help,

Sorry for answering this question late.

Diherdral scan can be done in gaussian with the help of gaussview. There is an option "modredundant" in the menu of gaussview. There is a symbol " R (within a square) ". Select this option it will prompt you to select options on which PES scan should be done such as angle, dihedral etc, choose the appropriate atoms in the molecule. Give number of steps and step size of angle. After that select gaussian setup and in the jobtype menu select scan and run the simulation. After the simulation load log file in gaussview, go to results menu in gaussview select scan.