Reynier:

=A0 I would go back to the older way of doing things in Gaus= sian.=A0 Before Modredundant became popular you were able to do a POPT.

The you separated the coordinates into two sets, one constan= t: and one variable:=A0 I am stuck in the airport now and can’t look at = the manual. =A0I think you have to use the keyword opt=3Dz-matrix.

=A0 Regards, Dave Close.

From: owner-chemistry+closed=3D=3Detsu.edu#ccl.net [mailto:owner-chemistry+closed=3D=3Detsu.edu#ccl.net] On Behalf Of R= eynier Suardiaz del R=EDo reynier.suardiaz!^!gmail.com
Sent: Friday, September 24, 2010 3:27 PM
To: Close, David M.
Subject: CCL:G: freezen dihedrals in five-membered rings<= /span>

Dear D. Close

Many thanks for your answer, you was right. I typed the values of the dihed= rals with 6 decimal places exactly matching with those of the input structure. D= oing this, the geometry optimization have finished without problem in a few iterations. Now what I would like to do is the following: I want to generat= e diferent conformations of this furanose ring by changing the dihedrals (bet= ween permitted values without breaking of the ring) and partially optimize this structures (obtained by slightly changing the dihedral values) and keeping frozen the five dihedrals. When I try to do this using redundant coordinate= s in gaussian I obtained the same error message than before:

-------------
Iteration 99 RMS(Cart)=3D 0.00005822 RMS(Int)=3D 0.009555= 80
Iteration100 RMS(Cart)=3D 0.00005748 RMS(Int)=3D 0.009598= 25
New curvilinear step not converged.
Error imposing constraints
Error termination via Lnk1e in C:\G03W\l101.exe at Fri Sep 24 21:05:0= 6 2010.
Job cpu time: 0 days 0 hours 0 minutes 1.0 seconds.
File lengths (MBytes): RWF=3D 7 Int=3D 0 D2E=3D = 0 Chk=3D 8 Scr=3D = 1
--------------

even if I only change one dihedral from its original value (at the input geometry) in less than one degree, the calculation ends with the abov= e error message.
Does anybody knows how to do this in gaussian, I mean, changing the dihedra= l angles of a five memebered ring (from its text input file) and to performe = a partial geometrical optimization with diferent dihedral angles, other than = the one of the input geometry?
any comment or suggestions are welcome.

thanks in advance and with very best regards

Reynier

2010/9/22 Close, David M. CLOSED~!~mail.etsu.edu <owner-chemistry= ]*[ccl.net>

Sent to CCL by: "Close, David M." [CLOSED#,#mail.etsu.edu]
Reynier:
There is no limit to how many dihedrals you can freeze. The pro= blem is that you typed something wrong. Notice that the program tried 99 iterations to fit you frozen coordiate information into the optimization routine.
Either you connected the coordinates incorrectly, or did not have enough precision in the frozen coordinate.
So if the input line has something like 10 5 6 8 31.3, first look at= the string 10 5 6 8 and make sure this is correct. The use a graphics pro= gram to examine the actual dihedral geometry. Run through the 4 atoms in t= he string 10 5 6 8 and see what the graphic program thinks the dihedral angle actually is. Copy the value to 5-6 decimal places and re enter the da= ta.
If this doesn't work, then you have to use trial and error. You said that freezing 2 dihedrals works. But how many iterations did it take? I would expect only 2-3. If more, then refine the coordinates, and then add a third frozen dihedral. You can quickly fi= nd the offending entry when the optimization routine bombs.
Regards, Dave Close.

________________________________________
> From: owner-chemistry+closed=3D=3Detsu.edu[A]ccl.net [owner-chemistry+clos= ed=3D=3Detsu.edu[A]ccl.net] on behalf of Reynier Suard az reynier.suardi= az(a)gmail.com [owner-chemistry[= A]ccl.net]
Sent: Wednesday, September 22, 2010 10:49 AM
To: Close, David M.
Subject: CCL:G: freezen dihedrals in five-membered rings

Sent to CCL by: "Reynier Suard az" [reynier.suardiaz]= _[gmail.com]
Dear All

I want to generate a lot of conformations of furanose ring (or cyclopentane= ?) and later partially optimize them but keeping frozen the dihedral angles. I= am trying to use redundant coordinates in gaussian writing at the end of the i= nput gaussian file the desired dihedrals to keep frozen. I am receiving an error message when i try to keep frozen more than two dihedral angles (of the rin= g) at the same time. For example if I try to froze the five dihedrals of the r= ing I get the following message:

------
Iteration 99 RMS(Cart)=3D 0.00001156 RMS(Int)=3D 0.003099= 67
Iteration100 RMS(Cart)=3D 0.00001134 RMS(Int)=3D 0.003103= 85
New curvilinear step not converged.
Error imposing constraints
Error termination via Lnk1e in C:\G03W\l101.exe at Mon Sep 20 17:48:1= 7 2010.
Job cpu time: 0 days 0 hours 0 minutes 1.0 seconds.
File lengths (MBytes): RWF=3D 7 Int=3D &nbs= p; 0 D2E=3D 0 Chk=3D 7 Sc= r=3D 1
---------

I receive this error message even when I try to freeze the dihedral at the = same value they already have in the initial structure.

Is not possible what am I trying to do? How can I overcome this problem wit= h gaussian? Is there any other possibility to do this kind of partial optimization in five-membered rings? Note that I can not freeze all the dihedrals using optimization in internal coordinates (opt=3Dz-matrix with a separate input section of "constants") because of to define a z-matrix of a five-membered ring are necesary only two dihedrals, so I have= to use redundants.
any comments or sugestions would be appreciatte

thanks in advance and very best regards

Reynierhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.ne= t/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt

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