How to deduce "phase factor" or "fermion sign"?

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Hi,

I am running some MCSCF calculations in NWChem and need to know how to deduce the phase factors (aka fermion signs) for certain creation (or annihilation) operators acting on the configurations.

Say I have a two electron system (singlet), then, in the NWChem output, i get something like:

          Converged CI vector

   Index           Coefficient          Config. Occupation
         1          0.95452656          1  1
        14         -0.29442754          2  2


Now what I need to know is:

- What does "1 1" in the "Config. Occupation" column mean?
- What phase factor (or fermion sign) do I get when an annihilation operator (ai) acts on any, say, the "1 1" configuration?

What I thought was that "1 1" means that the first alpha and first beta spin orbitals are occupied in that configuration, giving the occupation number vector:
| Φ1 > = | 1 1 0 ... 0 > ("2 2" would then give | Φ14 > = | 0 0 1 1 0 ... 0 >)
(here the spin orbitals are sorted so that the first spin orbital is the first alpha spin orbital, the second spin orbital is the first beta spin orbital, the third spin orbital is the second alpha spin orbital and so on).
Now if a1 acts on | Φ1 > we should get:
a_{1} | \Phi_{1} > = +1~|0~1~0~\dots~0>
and if a2 acts on | Φ1 > we should get:
a_{2}|\Phi_{1}> = -1~|1~0~0~\dots~0>

Does anyone know what is wrong with the above?

Thanks


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