From wibke@theochem.uni-duesseldorf.de Mon Sep 8 08:22:53 1997 Received: from lithium.theochem.uni-duesseldorf.de for wibke@theochem.uni-duesseldorf.de by www.ccl.net (8.8.3/950822.1) id IAA01215; Mon, 8 Sep 1997 08:13:06 -0400 (EDT) Received: from caesium.theochem.uni-duesseldorf.de (caesium.theochem.uni-duesseldorf.de [134.99.82.7]) by lithium.theochem.uni-duesseldorf.de (8.8.3/8.8.3) with ESMTP id OAA11488; Mon, 8 Sep 1997 14:10:20 +0200 (MET DST) Received: (from wibke@localhost) by caesium.theochem.uni-duesseldorf.de (8.8.3/8.8.3) id OAA19160; Mon, 8 Sep 1997 14:10:20 +0200 (MET DST) Date: Mon, 8 Sep 1997 14:10:20 +0200 (MET DST) From: Wibke Sudholt Message-Id: <199709081210.OAA19160@caesium.theochem.uni-duesseldorf.de> To: chemistry@www.ccl.net Subject: CASSCF/CASPT2 question Cc: wibke@lithium.theochem.uni-duesseldorf.de Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-MD5: LrRRQ6/YT50Gy061+qSyFg== Dear CCLers, perhaps someone of you can help me with this problem: I am doing excited state CASPT2 calculations with a CASSCF reference on a medium size organic molecule. Sometimes different starting orbitals lead to different CASSCF results probably because of several wavefunction minima. I suppose that this can be caused by an unsufficient active space, but I would run out of time and computational resources if I enlarge it. I also do not want to use state average calculations. So I need a systematic criterion to choose safely the "right" results. I am thinking of the lowest CASSCF energy (variation principle) or the highest weight of the CASSCF reference in the CASPT2 calculation (lowest perturbation). What would you prefer? Or are there other criterions? Can I compare calculations with different active spaces in the same way? I hope this question is not too stupid, but the subject is still relatively new to me. Any suggestions or pointers to the literature would be welcome. I will try to summerize. Thank you very much in advance Dipl.-Chem. Wibke Sudholt Institute of Theoretical Chemistry Heinrich-Heine-University Duesseldorf Germany wibke@theochem.uni-duesseldorf.de