Molcas Forum

Soichi_Shirai

Member

Registered: 2021-06-15

Posts: 2

[SOLVED] Calculation of a dipole moment using CASPT2.

I just started to use OpenMOLCAS to calculate a dipole moment of a molecule at CASPT2 level.
As a simple example, the dipole moment of LiH molecule with r = 2.5 angstrom was calculated.
The input prepared is shown below.

&GATEWAY
 coord=lih_2.5.xyz
 basis=cc-pvdz
 group=nosym
&SEWARD
&RASSCF
  nactel = 2 0 0
  inactive = 1
  ras2 = 2
  ciroot = 1 1 1
&CASPT2
  multistate = 1 1
  density
  properties

Here, lih_2.5.xyz is;

2
test
Li 0.0  0.0  2.5
H  0.0  0.0  0.0

It's my understanding that, by using these inputs, the CASSCF calculation is firstly carried out and the CASPT2 calculation is subsequently executed. In the output file, dipole moments calculated at the CASSCF and the CASPT2 were both printed out as I expected. However, the values were almost the same.

1st one

      Dipole Moment (Debye):
      Origin of the operator (Ang)=    0.0000    0.0000    0.0000
                   X=  5.6240E-16               Y=  9.6648E-16               Z=  6.4593E+00           Total=  6.4593E+00

2nd one

      Dipole Moment (Debye):
      Origin of the operator (Ang)=    0.0000    0.0000    0.0000
                   X=  1.0157E-15               Y=  5.7734E-16               Z=  6.4408E+00           Total=  6.4408E+00

When I carried out MRCI calculations with other program, the dipole moment was substantially changed because of the incorporation of dynamical correlations. The calculated dipole moment at the CASSCF level was almost the same with the above value (6.4593 Debye), suggesting that the CASSCF calculation was successfully carried out.

How can I get the dipole moment at the CASPT2 level correctly? Should I use &FFPT? I reviewed related Q&A and tried, but I couldn't find a solution. Any advice and suggestions are appreciated. Thank you in advance for your help.

---

Sincerely,
Soichi Shirai in Japan.

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,085

Re: [SOLVED] Calculation of a dipole moment using CASPT2.

With FFPT you'd just perform two calculations with different "dipole" strengths and do the energy differentiation manually. For instance:

&GATEWAY
...
&SEWARD
...
&FFPT
  dipo = z -0.001
&RASSCF
...
&CASPT2
...
&FFPT
  dipo = z 0.001
&RASSCF
...
&CASPT2
...

And the dipole (z component), in atomic units, would be (E(0.001)-E(-0.001))/0.002, which gives me:
CASSCF: 6.4542 D
CASPT2: 6.7853 D

Soichi_Shirai

Member

Registered: 2021-06-15

Posts: 2

Re: [SOLVED] Calculation of a dipole moment using CASPT2.

Thank you for your response and instruction . I could obtain the same value! And the value is quite close to the result by MRCI.

I'm very grateful to you. Many thanks!

---

Sincerely,
Soichi Shirai in Japan.