From toukie %-% at %-% zui.unizh.ch Wed Sep 10 03:23:14 1997 Received: from zzmkgtw.zzmk.unizh.ch for toukie -x- at -x- zui.unizh.ch by www.ccl.net (8.8.3/950822.1) id CAA11804; Wed, 10 Sep 1997 02:37:53 -0400 (EDT) Received: by zzmkgtw.zzmk.unizh.ch; (5.65v3.2/1.3/10May95) id AA26727; Wed, 10 Sep 1997 08:37:53 +0200 Message-Id: <3.0.3.32.19970910084021.00688270:~at~:highdent> X-Sender: toukie |-at-| highdent (Unverified) X-Mailer: QUALCOMM Windows Eudora Light Version 3.0.3 (32) Date: Wed, 10 Sep 1997 08:40:21 +0200 To: chemistry-!at!-www.ccl.net From: "Hr. Dr. S. Shapiro" Subject: MOPAC Question: Summary Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Dear Colleagues, Some time ago I submitted a question regarding how to do a MOPAC 6.0 run on p-tolylacetylene, which has four atoms [C(ar)-C#C-H] all in a straight line. I am grateful for the plethora of responses that I received. Very briefly, four suggestions were made: (a) use the normal Z-matrix, just add "xyz" to the list of keywords. This didn't work. Maybe it's a quirk in the Win95 port of MOPAC 6.0 that I use, but when I tried this strategy the calculation aborted with an error msg. to the effect that the programme was very unhappy with C(ar)-C#C-H = 180 degrees. (b) alter the Z-matrix so that C(ar)-C#C-H =/= 180 degrees at the start of the calculation. Sorry, but my port of MOPAC wasn't fooled by this. As soon as the geometry found itself adjusted to C(ar)-C#C-H = 180 degrees, it was no-go. (c) alter the geometry of the C(ar)-C#C-H unit using dummy atoms. Indeed, this works, but I was hoping for a slightly simpler solution that playing around with dummy atoms if I could possibly help it. (d) use Cartesian coordinates as the input. This was the solution I ultimately adopted. I drew the desired structure using PCModel and saved it as a normal MOPAC Z-matrix. I converted the input to Cartesian coordinates using Babel 1.6 for DOS and very slightly edited it to make it compatible with my port of MOPAC. It ran it with my "normal" roster of keywords; I did _not_ need to include "xyz" for the programme to recognise that the input was in Cartesian coordinates or that the calculation was to proceed using Cartesian coordinates. When I did this, the calculation quickly came to the desired conclusion. Again, many thanks to the respondents who were generous enough to share their experience and expertise with me. Regards, S. Shapiro toukie -x- at -x- zui.unizh.ch P.-S.: A summary re my LUMO question is pending.