From harbowy@chemres.tn.cornell.edu Sat Dec 19 01:19:51 1992 Message-Id: <199212190619.AA17512@oscsunb.ccl.net> From: m.e. Subject: MOPAC c.i. calculation To: CHEMISTRY@ccl.net (computational chemists) Date: Sat, 19 Dec 92 1:18:02 EST Organization: Cornell Chem Grad Student I am a graduate student in Organic Chemistry trying to overcome his math- phobia and learn Physical Chemistry. Therefore I thank you in advance on helping me in theis goal. I have been performing calculations on systems involving Bergman Cyclization, and I have reached a point of confusion in the study of a simple enediyne system. When the enediyne is converted to the 1,4 benzene diradical, I realized that simple RHF is going to fail miserably in this respect. But on trying to understand the complexities of the OPEN and CI commands, I ran across the following problem. First, I tried a simple CI calculation using the following commands AM1 SYMMETRY BONDS VECTORS SINGLET OPEN(2,2) C.I.=(2,0) MECI which gave a Hf of 131.77 for the diradical. Of course, since I was unsure of the diradical's 'actual' multiplicity of the HOMO and LUMO, I thought that perhaps a simple mixing between those two might be insufficient. It was my (naive) assumption that mixing in more configuractions couldn't hurt, because if the contribution was small, things wouldn't be affected. So I tried OPEN(2,3) C.I.=(3,0) to mix another empty orbital. This gave a Hf of 134.70 (!) and then OPEN(2,4) C.I.=(4,0) gave 135.22 (!). The eigenvectors were very curious as follows eigenvector 2,2 2,3 2,4 13 -10.03 -9.86 -9.92 14 -5.93 -5.09 -4.39 15 -4.70 -3.80 -3.15 16 -0.15 -1.49 -1.40 17 0.59 0.45 -1.10 18 2.68 2.41 2.31 Now assuming double filling of all the orbitals, 14 would be the HOMO. It was my (again, naive) assumption that 14 and 15 would be (reasonably) degenerate in a biradical species such as this, and only the 2,4 calculation seems to come close to that. The states reported by MECI are as follows state multiplicity 2,2 2,3 2,4 1 singlet -5.40 -7.81 -9.27 2 triplet -5.17 -7.60 -9.05 ... and others. This seems reasonable for the biradical: the triplet and singlet states should be fairly close in energy, no? But if each subsequent state is being stabilized, why is my total heat of formation going up? And what EXACTLY am I looking at here? I would be grateful if anyone could xplain exactly what evil things I have done, or at least point me in the right direction concerning the literature on CI and such. And one other point: would it be a bad thing to do C.I. on say, ground state molecules? Isn't CI adding to the description of the electronic state of the molecule, and thus 'improving' the definition? My adviser has suggested that CI might be a little problem for semiempirical methods because it has been parameterized without it, and I would like a little more information from anyone willing to point me in the right direction. I apologize for my naivete, and thank you in advance, -- matt ----------------------------------------------------------------------------- |/ _ /\ Matthew Harbowy (ikf@lithium.tn.cornell.edu) |\ - /__\ "I'm the bear that went over the mountain" ----------------------------------------------------------------------------- What kind of rule Can overthrow a fool and leave the land with no stain? -Suzanne Vega From slawek@rutile.rutgers.edu Sat Dec 19 11:04:10 1992 Date: Sat, 19 Dec 92 11:03:37 EST From: slawek@rutile.rutgers.edu (Slawomir Blonski) Message-Id: <9212191603.AA19267@rutile.rutgers.edu> To: CHEMISTRY@ccl.net, strasner@organik.uni-erlangen.de Subject: Re: MM2: atom type 50 I am not familiar with the atom type 50, but there was a problem with inter- actions between 2 benzene rings using the MM2 force field: the attraction between benzenes in sandwich configuration was too strong comparing with the T-shaped dimer. For reference see: I.Pettersson & T.Liljefors Journal of Computational Chemistry 8 (1987) 1139 and the next paper in that issue by Allinger and a coworker. Slawomir Blonski From scsupham@reading.ac.uk Sat Dec 19 12:12:34 1992 From: scsupham@reading.ac.uk Date: Sat, 19 Dec 92 17:11:49 GMT Message-Id: <15211.9212191711@scsscsc3> To: CHEMISTRY@ccl.net Subject: Convert from HPGL to PostScript ? ---------- X-Sun-Data-Type: text X-Sun-Data-Description: text X-Sun-Data-Name: text X-Sun-Content-Lines: 10 Dear All, I realise this request isn't very chemical but here we go... I'd like to find a program that converts Hewlett-Packard GL files into PostScript format. Thanks for any help. john upham John Upham, Dept. of Chemistry, University of Reading, Berks., RG6 2AD, UK. Email: scsupham%susssys1.rdg.ac.uk@uk.ac (BITnet), scsupham@rdg.susssys1 (Janet) Voice: +44 734 875123 x7441 (day), Fax: +44 734 311610 ---------- X-Sun-Data-Type: default X-Sun-Data-Description: default X-Sun-Data-Name: .signature X-Sun-Content-Lines: 3 John Upham, Dept. of Chemistry, University of Reading, Berks., RG6 2AD, UK. Email: scsupham%susssys1.rdg.ac.uk@uk.ac (BITnet), scsupham@rdg.susssys1 (Janet) Voice: +44 734 875123 x7441 (day), Fax: +44 734 311610