Calculation of oscillator strength

Supriyo Santra

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May 31, 2021, 3:40:27 AM5/31/21

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Dear all,

I am doing a CASSCF calculation in molpro for one conjugated hydrocarbon, which belongs to the C2h point group. I need to calculate the oscillator strength for transition between the ground state and higher excited state. Both these state have dipole momemt value of zero.

Hence, I saw in the output file , after convergence of CASSCF job it is not printing the quantities like <2.1|DMX|1.1> which are required for oscillator strength calculation.

To calculate the dipole moment value the formula is given as

f01=2/3*(E1-E0)*(|<2.1|DMX|1.1>|²+|<2.1|DMY|1.1>|²+|<2.1|DMZ|1.1>|²)

How is it possible to calculate oscillator strength between two states having zero dipole moment?

Thank you for consideration,

Supriyo Santra

Jacky LIEVIN

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Jun 1, 2021, 3:24:24 AM6/1/21

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Dear Supriyo,

My previous message didn’t arrive on the mailing list because of a typo in the address. I now answering on the list.

I made a test calculation on a simple C2h test system, using the following command for calculating the lower singlet states of Ag, Au and Bu symmetries:

{multi;closed,2,,2;wf,14,1,0;wf,14,2,0;wf,14,3,0}

The output gives the correct selection rules of the DM (see previous message):

!MCSCF STATE 1.1 Dipole moment 0.00000000 0.00000000 0.00000000

Dipole moment /Debye 0.00000000 0.00000000 0.00000000

!MCSCF STATE 1.2 Dipole moment 0.00000000 0.00000000 0.00000000

Dipole moment /Debye 0.00000000 0.00000000 0.00000000

!MCSCF STATE 1.3 Dipole moment 0.00000000 0.00000000 0.00000000

Dipole moment /Debye 0.00000000 0.00000000 0.00000000

State-averaged charge density matrix saved on record 2140.2 (density set 1)

!MCSCF trans <1.3|DMX|1.1> 0.355019896640 au = 0.902311468903 Debye

!MCSCF trans <1.3|DMY|1.1> 0.693685973614 au = 1.763058396819 Debye

!MCSCF trans <1.2|DMZ|1.1> 0.140173697413 au = 0.356262665871 Debye

If you still have problems, please post the input file

Best wishes,

Jacky

Le 31 mai 2021 à 14:03, Supriyo Santra <supriyos...@gmail.com> a écrit :

Thank you for your response.
While doing the calculation, I have kept the orbitals of bg and au symmetry in the CAS space.
The direct product of bg and au produces an excited state of Bu symmetry. The molecule in the ground state is having Ag symmetry.
For the excited state of Bu symmetry all the components (along X,Y,Z) of the dipole moment are zero, which is also true for ground state Ag symmetry.
Then could you please suggest how can I get the terms like: < Ag | DMX and DMY | Bu > , as I am targeting a Bu excited state?
In general it is not printing in the output file, as it is printed in case when the components of the dipole moment are non-zero along one or multiple directions.

Thank you for your time and consideration
Supriyo Santra

On Mon, May 31, 2021 at 3:26 PM Jacky LIEVIN <guitar...@gmail.com> wrote:
Dear Supriyo,

A C2h molecule has an inversion and is centrosymmetric. Consequently, it has no dipole moment. Electric dipole transitions are nevertheless allowed, according to the appropriate selection rules of the dipole moment operator.

DMX and DMY belong to Bu and DMZ to Au. According to the direct product rules, the following transitions have non zero transition dipole moment value:
< Ag | DMZ | Au >
< Ag | DMX and DMY | Bu >
< Au | DMZ | Bg >
< Bg | DMX and DMY | Bu >

These transitions are polarized either along Z or along X,Y.

You should check these rules in your CASSCF calculations.

Best wishes,

Jacky Liévin

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Jacky LIEVIN

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Jun 1, 2021, 7:07:50 AM6/1/21

to molpro-user, Supriyo Santra

The problem is that you are calculating the 3 lowest states of Bu symmetry (symmetry 3) and that transitions are forbidden between Bu states according to the selection rules.

In a previous mail you mentioned that you were interested by the transitions between the Ag ground state and excited Bu states?

The cassf command should then be:

{cassf

orbital,2140.2

icc,16,5,15,5

closed,16,0,15,0

wf,72,2,0; ! Ag ground state

wf,72,3,0; state,3 ! Bu excited states

print,nature}

Jacky

Le 31 mai 2021 à 18:43, Supriyo Santra <supriyos...@gmail.com> a écrit :

Thank you for your response again. I am still facing the problem , as I am unable to detect what I am missing in my input file. I am attaching the input file below, please have a look at it.

memory,50000,M
file,2,casscf_3bu.wfu,new
print,basis,orbital
geometry={
C 5.5540545578 0.2194300988 0.0000000000
H 5.6266148200 1.2939012936 0.0000000000
H 6.4764651499 -0.3326422846 0.0000000000
C 1.8810829590 -0.3576531342 0.0000000000
C 0.5977104860 0.3201210827 0.0000000000
C -0.5977104860 -0.3201210827 0.0000000000
C -1.8810829590 0.3576531342 0.0000000000
C -3.0761675446 -0.2794035661 0.0000000000
C -4.3629012171 0.4068539279 0.0000000000
C -5.5540545578 -0.2194300988 0.0000000000
C 3.0761675446 0.2794035661 0.0000000000
C 4.3629012171 -0.4068539279 0.0000000000
H 4.3373734768 -1.4851377368 0.0000000000
H 3.0975421090 1.3582120284 0.0000000000
H 1.8643953200 -1.4366722318 0.0000000000
H 0.6133098003 1.3990455034 0.0000000000
H -0.6133098003 -1.3990455034 0.0000000000
H -3.0975421090 -1.3582120284 0.0000000000
H -1.8643953200 1.4366722318 0.0000000000
H -4.3373734768 1.4851377368 0.0000000000
H -5.6266148200 -1.2939012936 0.0000000000
H -6.4764651499 0.3326422846 0.0000000000
}
basis = 6-311++g(d,p)
{hf
wf,72,1,0}

{casscf
orbital,2140.2
occ,16,5,15,5
closed,16,0,15,0
wf,72,3,0; state,3
print,natorb}

On Mon, May 31, 2021 at 8:46 PM Jacky LIEVIN <guitar...@gmail.com> wrote:
It seems that I have problems with molpro-user
Please find my answer

Jacky Liévin

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