Small wheight of reference WF in CASPT2

Posted by Evgeniy on October 02, 2008 at 17:23:18:

Dear CASSCF/CASPT2 Gurus,

I am wondering whether the weight 0.57 of the reference wavefunction in CASPT2 should be considered as being too small to give a reliable energy. I obtain this weight for both the ground and lowest excited state, with the zero oder WF being SA2-CASSCF(10,10). I tried to apply SHIFT=0.1 and 0.2 which gave the increase of the wheight to 0.6. Should the imaginary shift ("Imaginary") work better in this case? Could it be that the problem has to do with the fact that my system is an anion (charge -1), although the ground state and the lowest excited state are of valence character (not Rydberg states) and therefore I don't use diffuse functions in the basis set? Many thanks in advance for your replies!

Best regards,
Evgeniy

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Re: Small wheight of reference WF in CASPT2 Coen de Graaf 09:38:59 10/03/08 (0)

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: Dear CASSCF/CASPT2 Gurus, : I am wondering whether the weight 0.57 of the reference wavefunction in CASPT2 should be considered as being too small to give a reliable energy. I obtain this weight for both the ground and lowest excited state, with the zero oder WF being SA2-CASSCF(10,10). I tried to apply SHIFT=0.1 and 0.2 which gave the increase of the wheight to 0.6. Should the imaginary shift ("Imaginary") work better in this case? Could it be that the problem has to do with the fact that my system is an anion (charge -1), although the ground state and the lowest excited state are of valence character (not Rydberg states) and therefore I don't use diffuse functions in the basis set? Many thanks in advance for your replies! : Best regards, : Evgeniy

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