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Matthieu Sala
matthieu.sala@u-bourgogne.fr

I am studying the photochemistry of the aniline molecule (Ph-NH2) using the XMCQDPT2 method, and I have trouble to obtain accurate values for the oscillator strengths, partial charges and dipole moments in the two first pipi* excited states.

In a previous CASSCF study, the first pipi* state has been assigned as a local excitation while the second as a charge transfer state with ca. 0.2 electron transfered from the N atom to the C atom at the opposite part of the ring.
Moreover, accurate values (in comparison with experiments) for the oscillator strength has been reported at the SAC-CI, TD-CAMB3LYP and EOM-CCSD levels of theory. Experimental values are 0.028 for the 1pipi* and 0.144 for the 2pipi* states.

I use a minimal active space of 8 el in 7 orb (3pi, 3pi* and the N lone pair) to describe excited pipi* states. I use a SA3-CASSCF reference wavefunction.
Then I performed XMCQDPT2 calculations with increasing size of the model space (3, 10 and 20).

I have several problems. First Mulliken and Lowdin charge analysis give very different results (I think the Lowdin is more reasonnable).
Second the dipoles, oscillator strength and partial charges change a lot when the model space size is increased. For NSTATE=3 in XMCQDPT2, the results are quite close from what we can expect (although the oscillator strength for the 1pipi* state is significantly underestimated).
But when NSTATE is increased, the results change a lot. The oscillator strengths are greatly overestimated and the first pipi* state seems to acquire a charge transfer character.

Could someone tell me what am I doing wrong ?
Any help would be greatly appreciated.

I attach the inputs and output of the XMCQDPT2 calculations
(all merged in one text file).

Best regards.
Matthieu Sala

This message contains the 2897 kb attachment [ xmcqdpt2.txt ] XMCQDPT2 with NSTATE=3,10,20. Inputs and outputs merged.