Mr. Ruzi,

The dipole strengths are obtained directly using Freq=(vcd,vibrot). The magnitude value determins the length of the arrow of the dipole moment vector. The polarizability tensor components and the depolarization ratios provide you information about the direction. Thus, (alpha)xx and (alpha)yy provide you information about the dipole moment induced in the corresponding directions x and y, respectively. You could see the basic equations determining the induced dipole moment and depolarization ratio in any monograph/textbook devoted to polarized IR (or Raman) spectroscopy. You should add "output=pickett" (http://www.gaussian.com/g_tech/g_ur/k_output.htm). The output-data have the well known tabular form.

For H2O, for example, the analysis by HF/6-31G (Freq=(VCD,vibrot) output=pickett) is:

A' A' A'

Frequencies -- 1794.3229 4127.3273 4227.0497

Red. masses -- 1.0867 1.0414 1.0819

Frc consts -- 2.0614 10.4525 11.3895

IR Inten -- 101.5986 2.4780 28.0413

Raman Activ -- 11.7870 84.5429 45.8728

Depolar (P) -- 0.4093 0.1998 0.7500

Depolar (U) -- 0.5809 0.3331 0.8571

Dip. str. -- 225.8887 2.3952 26.4648

Rot. str. -- 0.0000 0.0000 0.0000

Thanks,  Dr Ivanova. 

I need to run the water example to see if it gives me the information I'm after.

I found out that an iop(7/33=1) needs to be included to calculate transition dipole moments.

Take water molecule for example:

%chk=water.chk

#p  hf/6-31G opt

---

water charge and geom specifications

---

--link1--

%chk=water.chk

#p hf/6-31G geom=allcheck guess=read freq iop(7/33=1) 

---

i.e., the opt and freq can not be in the same input, otherwise it does not work. It should be linked (via link1).

The output gives du/dQ(x,y, and z) as 'Dipole derivatives wrt mode 1: du/dQ(x)  du/dQ(y)   du/dQ(z)  in units of (Km/mol)^0.5, i.e. the same units as the square root of intensity.  It can be converted to the more common used units Debye per angstrom pers squareroot of amu by dividing by 6.5005.

Hello, use this:

Case of Water(H2O)

Input look like this:

# b3lyp/6-31g freq freq iop(7/33=1)

Output look like this:

Dipole derivative wrt mode 1: -1.29096D-14 -2.16863D+02 -1.22125D-14 Dipole derivative wrt mode 2: 9.34335D-16 0.00000D+00 -3.68709D+00 Dipole derivative wrt mode 3: -4.22412D-15 -1.06581D-13 -1.26465D+01

Hope This Helps,

Regards

Ajay khanna

Dear Mr Ruzi,

would it be possible to provide some ressources, which give information on the units of the dipole derivatives in Gaussian and on the conversion factor of 6.5005 you mentioned above? For me it is not clear, how you found this conversion factor.

It would help to improve understanding of what Gaussian actually calculates.

With best wishes,

Eric Fischer