From owner-chemistry@ccl.net Sun Jul 28 11:03:00 2013 From: "Laidig, Bill laidig.wd|*|pg.com" To: CCL Subject: CCL: error in Diels Alder reaction TS Message-Id: <-49029-130728110152-1157-tMaeQ+eMC+ua/6Ci1lVwoA^_^server.ccl.net> X-Original-From: "Laidig, Bill" Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_36CA2139DC37984ABAA757CF441D8320337130BFGADCEMB025napgc_" Date: Sun, 28 Jul 2013 15:01:44 +0000 MIME-Version: 1.0 Sent to CCL by: "Laidig, Bill" [laidig.wd\a/pg.com] --_000_36CA2139DC37984ABAA757CF441D8320337130BFGADCEMB025napgc_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable 2 things to try: 1) Added the keyword HESS=3D3-21G to the options line in the setup dia= log. This will give you a HF/3-21G analytic hessian as your starting hessi= an. 2) If this still does not converge do a single point hybrid-DFT with 6= -31G(D) and check the IR box. This job will generate the exact hessian at = the starting geometry. Next redo the TS calc (make sure the HESS=3D keywor= d is deleted). > From: owner-chemistry+laidig.wd=3D=3Dpg.com.^_^.ccl.net [mailto:owner-chemistry= +laidig.wd=3D=3Dpg.com.^_^.ccl.net] On Behalf Of Olasunkanmi Lukman Olawale wal= ecomuk _ yahoo.co.uk Sent: Friday, July 26, 2013 8:30 AM To: Laidig, Bill Subject: CCL: error in Diels Alder reaction TS Dear All, I tried to run calculations on the transition state geometry of some simple= Diels Alder reactions using hybrid-DFT with 6-31G(D) (and others) basis se= ts. I am using SPARTAN 10. All the attempts I have made has always been giv= en me error messages e.g. maximum optimization cycles reached. Can you plea= se share your experience with me in running this kind of calculations? I wi= ll also appreciate if there is any material that explains the steps in runn= ing such calculations. Thank you. Lukman. ________________________________ --_000_36CA2139DC37984ABAA757CF441D8320337130BFGADCEMB025napgc_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

2 things to try:

<= /p>

1) = ; Added the keyword= HESS=3D3-21G to the options line in the setup dialog. This will give= you a HF/3-21G analytic hessian as your starting hessian.

2) = ; If this still doe= s not converge do a single point hybrid-DFT with 6-31G(D) and check the IR = box. This job will generate the exact hessian at the starting geometry. Next redo the TS calc (make sure the HESS=3D keyw= ord is deleted).

<= /p>

From: owner-ch= emistry+laidig.wd=3D=3Dpg.com.^_^.ccl.net [mailto:owner-chemistry+laidi= g.wd=3D=3Dpg.com.^_^.ccl.net] On Behalf Of Olasunkanmi Lukman Olawale walecomuk _ yahoo.co.uk
Sent: Friday, July 26, 2013 8:30 AM
To: Laidig, Bill
Subject: CCL: error in Diels Alder reaction TS

Dear All,

I tried to run calculations on the tran= sition state geometry of some simple Diels Alder reactions using hybrid-DFT= with 6-31G(D) (and others) basis sets. I am using SPARTAN 10. All the attempts I have made has always been given me error messages e= .g. maximum optimization cycles reached. Can you please share your experien= ce with me in running this kind of calculations? I will also appreciate if = there is any material that explains the steps in running such calculations. Thank you.

<= /o:p>

Lukman.=

--_000_36CA2139DC37984ABAA757CF441D8320337130BFGADCEMB025napgc_-- From owner-chemistry@ccl.net Sun Jul 28 12:49:00 2013 From: "Alan Shusterman alan/a\reed.edu" To: CCL Subject: CCL: error in Diels Alder reaction TS Message-Id: <-49030-130727194919-8109-wIBCVCKS93nm0cmq+tRIRg.:.server.ccl.net> X-Original-From: Alan Shusterman Content-Type: multipart/alternative; boundary="------------040504050102080603020800" Date: Sat, 27 Jul 2013 16:49:10 -0700 MIME-Version: 1.0 Sent to CCL by: Alan Shusterman [alan _ reed.edu] This is a multi-part message in MIME format. --------------040504050102080603020800 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Dear Lukman, If your Diels-Alder reactants are structurally complicated (large substituents) then the problem might lie in the starting structure of the substituents. Try this: 1. Search for the TS of 1,3-butadiene + ethylene in the Spartan TS database (the tutorial book can show you how to do this) 2. Freeze all six C atoms 3. Build the rest of your system by adding whatever atoms are needed 4. Calculate the Equilibrium Geometry *subject to the Frozen Atom constraint* (this will help the non-frozen substituents relax into an equilibrium geometry; warning: there may be more than one conformation for these substituents and you will have to try each one separately if you wish to learn about these) 5. Finally, once the substituents have been optimized, search for a Transition State *WITHOUT* the Frozen Atom constraint. You may want to calculate the IR spectrum before you attempt this and verify that the Diels-Alder reaction coordinate is still recognized with a large imaginary frequency. This approach nearly always works, but some things can throw it off. For example, if your Diels-Alder TS is highly asynchronous. In that case, a more incremental approach might be needed. Good luck, Alan On 7/26/13 5:29 AM, Olasunkanmi Lukman Olawale walecomuk _ yahoo.co.uk wrote: > Dear All, > I tried to run calculations on the transition state geometry of some > simple Diels Alder reactions using hybrid-DFT with 6-31G(D) (and > others) basis sets. I am using SPARTAN 10. All the attempts I have > made has always been given me error messages e.g. maximum optimization > cycles reached. Can you please share your experience with me in > running this kind of calculations? I will also appreciate if there is > any material that explains the steps in running such calculations. > Thank you. > Lukman. > ------------------------------------------------------------------------ > ** -- Alan Shusterman Chemistry Department Reed College Portland, OR 97202-8199 503-517-7699 http://blogs.reed.edu/alan/ "Nature doesn't make long speeches." Lao Tzu 23 --------------040504050102080603020800 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Dear Lukman,

If your Diels-Alder reactants are structurally complicated (large substituents) then the problem might lie in the starting structure of the substituents. Try this:

1. Search for the TS of 1,3-butadiene + ethylene in the Spartan TS database (the tutorial book can show you how to do this)
2. Freeze all six C atoms
3. Build the rest of your system by adding whatever atoms are needed
4. Calculate the Equilibrium Geometry subject to the Frozen Atom constraint (this will help the non-frozen substituents relax into an equilibrium geometry; warning: there may be more than one conformation for these substituents and you will have to try each one separately if you wish to learn about these)
5. Finally, once the substituents have been optimized, search for a Transition State WITHOUT the Frozen Atom constraint. You may want to calculate the IR spectrum before you attempt this and verify that the Diels-Alder reaction coordinate is still recognized with a large imaginary frequency.

This approach nearly always works, but some things can throw it off. For example, if your Diels-Alder TS is highly asynchronous. In that case, a more incremental approach might be needed.

Good luck,

Alan

On 7/26/13 5:29 AM, Olasunkanmi Lukman Olawale walecomuk _ yahoo.co.uk wrote:

Dear All,

I tried to run calculations on the transition state geometry of some simple Diels Alder reactions using hybrid-DFT with 6-31G(D) (and others) basis sets. I am using SPARTAN 10. All the attempts I have made has always been given me error messages e.g. maximum optimization cycles reached. Can you please share your experience with me in running this kind of calculations? I will also appreciate if there is any material that explains the steps in running such calculations. Thank you.

Lukman.

-- 
Alan Shusterman
Chemistry Department
Reed College
Portland, OR 97202-8199
503-517-7699
http://blogs.reed.edu/alan/
"Nature doesn't make long speeches." Lao Tzu 23

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