Posted by Steven on September 19, 2012 at 09:32:43:

In Reply to: Calculation of dipole moments posted by Andy Kerridge on September 29, 2011 at 18:49:43:

: Hi,

: I'm trying to calculate the dipole moment of NiH, which has been done previously using CASSCF (J. Chem. Phys. 101:4893, 1994). My CASSCF value is approximately 3D, in general agreement with the CASSCF value quoted in the paper of 3.1D. However, in the paper a refined value of 2.65 is obtained using CASPT2. My CASPT2 calculated value is essentially the same as my CASSCF one, in fact a little larger. I am using the DENSITY keyword in CASPT2, as recommended in the manual. Can someone explain why do I not see an improvement in my calculated value? I notice that the dipole moment is calculated using a perturbative approach in the paper, but my output gives an expectation value for the dipole moment. Is this the cause of the difference? I understand that FFPT can be used in order to obtain a perturbative result, but can anyone tell me how the calculation is actually performed?

: Regards,

: Andy

The perturbative approach is to calculate the CASPT2 energies at different field strengths, then you have a set of points F,E(F) from which you can deduce the dipole moments and other properties. So basically, you get the energy in function of the field strength and go from there.