Molcas Forum

gilbert

Member

From: Rostock

Registered: 2016-10-12

Posts: 5

differences between the rassi and rasscf wave functions

Dear all,

I am from time to time observing the following behaviour of the molcas rassi and rasscf wave-functions:
Suppose, I have an optimized rasscf wave function for the lowest 10 states of e.g. the singlet beryllium atom.
Now I run a rassi calculation to get the transition dipole moments. Note that I am using only one JobIph file, e.g. one CI wave-function for this.
When I compare the dipole matrix calculated between the original rasscf states (keyword MEIN) with the one calculated for the spin-free rassi states (keyword MEES), I see notable differences in the order of 10 %. Interestingly sometimes transitions that were forbidden between the rasscf states become possible in the basis of spin-free rassi states.
This implies that the rassi spin free state basis is different from the rasscf basis. while this is clear as soon as multiple rasscf wavefunctions are to be combined in rassi, I do not understand it for the case when I have only a single rasscf wave function.

Note: one can notice slight energy differences between the rasscf and rassi energies as well.

My question is: How can I understand that the basis of spin-free rassi states that is obtained from a single rasscf wave-function is different from the rasscf basis?

To my mind the only explanation is that the Hamiltonian is not diagonal in the basis of the rasscf states. However, this seems odd as it implies that the rasscf states are no eigenstates to the Hamiltonian.

I hope that my point is clear. Thanks for any response.

PS: I rely on the CI expansion of the spin-free states for further processing. If anyone knows, how one can access the coefficients for the rassi spin=free states, I would be very grateful.

Last edited by gilbert (2016-10-12 16:09:36)

tumitumi123

Member

Registered: 2017-06-13

Posts: 16

Re: differences between the rassi and rasscf wave functions

Hi
Have you solve this problem, do you know the answer. I have the same question as you are.
Shan

Hanros

Member

Registered: 2017-12-26

Posts: 17

Re: differences between the rassi and rasscf wave functions

Hi

Did anyone get an answer to this.