From chemistry-request#* at *#server.ccl.net Wed Apr 3 10:20:11 2002 Received: from nikias.cc.uoa.gr ([195.134.68.10]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id g33FKAp18285 for ; Wed, 3 Apr 2002 10:20:10 -0500 Received: from localhost (jkerkin \\at// localhost) by nikias.cc.uoa.gr (8.9.3/8.9.3) with SMTP id SAA05318 for ; Wed, 3 Apr 2002 18:20:00 +0300 (EET DST) Date: Wed, 3 Apr 2002 18:20:00 +0300 (EET DST) From: Ioannis Kerkines To: chemistry -x- at -x- ccl.net Subject: G98 CASSCF Efficiency Considerations Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear listmembers, I am trying to perform with Gaussian 98 a CASSCF calulation with 4 electrons in 4 orbitals for a diatomic molecule using a basis set of 224 functions. I have encountered many problems so far regarding efficiency and I would like to ask if anybody has any experience with this. First of all, I am unable to do a "conventional" (SCF=Conven) calculation because I have g functions in the basis set, whereas the subroutine performing "conventional" calculations suppotrs only up to f functions. The direct calculation of integrals needs much memory which is not available. In fact I get a message: InCore calculation needs more space: 341070520 In this calculation the integrals will be calculated in every iteration and Contracted with The Density Matrices so the actual ("direct") calculation needs very much time to be done. Furthermore, the CASSCF iterations after approaching convergence (very very slowly), they start to diverge (very very slowly again), until reaching the max. no of iterations (64 in this case) and then stop. I tried to change the convergence options by imposing quadratic convergence ( (CASSCF,4,4,QC,FullDiag) but no luck, I get an error message at the beginning of the iterations) or Davidson Diagonalization (same convergence behaviour as mentioned above). I also use a very good guess (I have compared it with Molpro which takes so much less time and converges easily). Does anybody have any experience with this? Best regards, Ioannis