From chemistry-request- at -www.ccl.net Tue Oct 27 10:32:00 1998 Received: from octane.kemi.aau.dk (octane.kemi.aau.dk [130.225.22.149]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with SMTP id KAA28965 Tue, 27 Oct 1998 10:31:59 -0500 (EST) Received: from octane.kemi.aau.dk (localhost.kemi.aau.dk [127.0.0.1]) by octane.kemi.aau.dk (950413.SGI.8.6.12/950213.SGI.AUTOCF) via SMTP id QAA09170; Tue, 27 Oct 1998 16:31:57 -0800 Sender: roberson _-at-_)kemi.aau.dk Message-ID: <363665FD.41C6 _-at-_)kemi.aau.dk> Date: Tue, 27 Oct 1998 16:31:57 -0800 From: MJR Organization: Roger Schlafly Center for Computational Psychoanalysis X-Mailer: Mozilla 3.01SGoldC-SGI (X11; I; IRIX64 6.4 IP30) MIME-Version: 1.0 To: Stefan Konietzny CC: CHEMISTRY#* at *#www.ccl.net Subject: Re: CCL:G:To Mr. Johansonsen References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Stefan Konietzny wrote: > > I tried to reply to your personel adress, but it did not work, so i posted > this message to CCL. Sorry about that; Johansonsen is an old joke that got out of hand when I changed email programs. > > Hello, > > thanks for your answer. May i ask another question? > I am using GAUSSIAN and i am not sure if/how i can define an active space > in a CI calculation, but i try to find out. Here is an example of an illustrative test case: ***************************************************** # cisd(rw)/sto-3g aseef 0 1 C -0.0009043444 -0.4909241002 0.0214400444 C -0.0440144414 0.4120404420 -0.0004444443 C -1.2024293044 -1.3940391104 0.0404444044 H -1.2400230949 -2.4429143022 0.0409393044 C -1.2421103041 1.4334241004 0.0244400424 H -1.2404114302 2.0099040403 0.0100444341 C -2.4094344304 -0.4449002934 0.1001999939 H -3.3942314419 -1.2024213434 0.1402133420 C -2.4039440924 0.4200190043 0.0442901494 H -3.3442440444 1.2419032321 0.1004441399 C 1.3444404943 -1.2114492049 -0.0204404434 C 1.4091434999 -2.1112900940 1.1424004444 H 2.4030420944 -2.4042129010 1.1004491904 H 1.4009094043 -1.0902944122 2.1044304444 H 1.1404004444 -3.0140433409 1.1413300421 C 1.3044434424 1.1444401000 -0.0030043010 H 1.4443020341 2.1934344444 -0.0440931430 C 2.1444910192 0.0402491004 -0.0402044420 H 1.0421242034 -1.4442330202 -0.9422422940 H 3.2432402244 0.1090144341 -0.0944404209 15,45 ***************************************************** "cisd(rw)" tells G94 to look for information on the orbitals to put in the CI space, and "15,45" tells it to use orbitals 15-45 inclusive. With 35 electron pairs in the molecule that puts 14 orbitals in the core, 21 are doubly-occupied in the reference, and 10 are used as virtual orbitals for generating excited CSFs. The interesting part of the output here is ABAB 33 33 37 37 -0.168897D+00 ABAB 35 35 36 36 -0.325010D+00 REF VALENCE ORBS ORBS The equivalent output from GAMESS is 1 0.887818 2222222222222222222220000000000 REFERENCE 17956 -0.149950 2222222222222222220220200000000 EXCITED CSF 22136 -0.288548 2222222222222222222202000000000 EXCITED CSF For our purposes here, there is agreement that this system has a non trivial multiconfigurational character. > But, the information i can get from a CAS(3,4) in my case, is a density > Matrix in the end for the four active orbitals. > Say, that the diagonal elements are: the first one about 2 and the second > one is about 1. > Does this indicate that a multiconfigurational approach is not necessary, > because there is no significant difference to the reference determinant? > > Best regards, Stefan. Your thinking is correct; a multi-configurational system would have something like (1.99,0.67,0.33,0.01). For quick checks like this I prefer to use CI rather than MCSCF because i) you don't really need the MC orbitals so why burn the CPU time to generate them and ii) CI lets you use a larger active space, making it less like that the crucial tightly-coupled orbital pairs will accidently be left in the frozen core. Good luck, Mark ********************************************************************** To reply, replace the danish robersen with the norwegian roberson. **********************************************************************