From owner-chemistry@ccl.net Sat Dec 10 11:17:00 2011 From: "Thomas Exner thomas.exner%a%uni-konstanz.de" To: CCL Subject: CCL: CASSCF problems Message-Id: <-46019-111210091028-16286-WGjVCRvdpdQjs7YULJcHcw++server.ccl.net> X-Original-From: Thomas Exner Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-15; format=flowed Date: Sat, 10 Dec 2011 15:09:44 +0100 MIME-Version: 1.0 Sent to CCL by: Thomas Exner [thomas.exner%%uni-konstanz.de] Dear CCLers: I am running in some problem with CASSCF calculations using g09, for which I have no explanation, and I hope that somebody out there can help me. I would like to start with a relative simple system: NO. For this system I would expect that the unpaired electron is distributed equally between the two antibonding pi orbitals. But I get an occupation number of exactly 1 for the first and 0 for the second orbital using a casscf(1,2) calculation. In a casscf(5,4) including the two bonding pi orbitals, there is again almost exactly 1 electron in the one orbital and a few percent of an electron in the other. The additional electron occupation is taken from the bonding orbitals. Has somebody an idea, what I am going wrong, or is my assumption of equal distribution wrong? Here is the input (pretty simplex, eh): # casscf(5,4)/sto-3g nosymm NO 1 0 2 O N 1 B1 B1 1.25247685 Additionally, I have a larger system for which I also perform casscf calculations. Ground state simulations and also the first excited state using the ground state geometry are fine. Energy optimization in the excited state also starts ok but after some steps the calculation does not converge anymore. Use of "use=l506" as proposed in the g09 manual did not help. Also no luck with increasing the maxcycle or starting with an other conformation. Is there anything else I can try? Perhaps there are some options for the optimizer that he does not jump into the bad region with the convergence problems. Unfortunately, the "sleazy" and the "qc" keyword for scf cannot be used with casscf optimization. Any help is highly appreciated. Best. Thomas From owner-chemistry@ccl.net Sat Dec 10 15:51:00 2011 From: "=?iso-8859-1?Q?J=FCrgen_Gr=E4fenstein?= jurgen**chem.gu.se" To: CCL Subject: CCL:G: CASSCF problems Message-Id: <-46020-111210152524-1627-i8B95ybVcWd4sX7+ogk/5w(0)server.ccl.net> X-Original-From: =?iso-8859-1?Q?J=FCrgen_Gr=E4fenstein?= Content-ID: Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="iso-8859-1" Date: Sat, 10 Dec 2011 20:25:10 +0000 MIME-Version: 1.0 Sent to CCL by: =?iso-8859-1?Q?J=FCrgen_Gr=E4fenstein?= [jurgen:_:chem.gu.se] Dear Thomas, Everything appears to be all right. The state you seek is twofold degenerate (Pi_x, Pi_y), and a quantum chemical calculation gets you one of the states. In order to get an equal distribution between Pi_x and Pi_y you would need a fractional-occupation-number (FON) CASSCF. I am not sure whether something like this has been worked out and implemented somewhere for CASSCF. (FON-DFT is implemented in Gaussian). Best regards, Jürgen ---- Jürgen Gräfenstein University of Gothenburg Dept of Chemistry Jurgen.Grafenstein!A!chem.gu.se On 10 Dec, 2011, at 15:09 , Thomas Exner thomas.exner%a%uni-konstanz.de wrote: > > Sent to CCL by: Thomas Exner [thomas.exner%%uni-konstanz.de] > Dear CCLers: > > I am running in some problem with CASSCF calculations using g09, for which I have no explanation, and I hope that somebody out there can help me. I would like to start with a relative simple system: NO. For this system I would expect that the unpaired electron is distributed equally between the two antibonding pi orbitals. But I get an occupation number of exactly 1 for the first and 0 for the second orbital using a casscf(1,2) calculation. In a casscf(5,4) including the two bonding pi orbitals, there is again almost exactly 1 electron in the one orbital and a few percent of an electron in the other. The additional electron occupation is taken from the bonding orbitals. Has somebody an idea, what I am going wrong, or is my assumption of equal distribution wrong? > > Here is the input (pretty simplex, eh): > # casscf(5,4)/sto-3g nosymm > > NO 1 > > 0 2 > O > N 1 B1 > > B1 1.25247685