From owner-chemistry@ccl.net Sat Dec 1 05:38:01 2007 From: "marcel.swart*icrea.es" To: CCL Subject: CCL: spin changes through the reaction Message-Id: <-35742-071201052252-791-o80D67vVBtiLxWnyey+vTg[a]server.ccl.net> X-Original-From: marcel.swart#icrea.es Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8; DelSp="Yes"; format="flowed" Date: Sat, 1 Dec 2007 11:22:39 +0100 MIME-Version: 1.0 Sent to CCL by: marcel.swart-.-icrea.es > I think you two have arrived in agreement with each other already. > Spin-inversion is a nonadiabatic process and requires an inspection =20 > for a crossing seam on the different potential energy =20 > surfaces.However, as suggest by Dongqi Wang, the excitation of A to =20 > another spin state, for example from singlet to triplet can also =20 > happen first. That is exactly what Zhu described in Eq (1) and (2). =20 > How to determine the crossing seams between the potential energy =20 > surfaces of different spin state is pretty tricky. a simple approach =20 > to > approximately locate the crossing points is to analysize the =20 > potential energy surfaces with diffrent spin state. In my memory, =20 > there are two references in this topic. I hope they are helpful to =20 > you. > (1)Yoshizawa, K.; Shiota, Y.; Yamabe, T. J. Chem. Phys. 1999,111, 538. > Yoshizawa, K.; Kagawa, Y. J. Phys. Chem. A 2000, 104, 9347. > (2)Zhang G.-B.; Li S.-H. Organometallics 2003, 22, 3820 Also have a look at the work by Sason Shaik and co-workers, who looked at the doublet-quartet crossing in some papers; the called it the "two-state reactivity". See for instance: J.Am.Chem.Soc. 2006, 128, 8590-8606 (and references therein) From owner-chemistry@ccl.net Sat Dec 1 06:37:00 2007 From: "mohamed aish mhmdaish!^!yahoo.com" To: CCL Subject: CCL: basis set erroneous concept Message-Id: <-35743-071201063545-28832-dUgs6+uhT+480Ayo76rvnA|*|server.ccl.net> X-Original-From: mohamed aish Content-Transfer-Encoding: 8bit Content-Type: multipart/alternative; boundary="0-951450408-1196508934=:96939" Date: Sat, 1 Dec 2007 03:35:34 -0800 (PST) MIME-Version: 1.0 Sent to CCL by: mohamed aish [mhmdaish{=}yahoo.com] --0-951450408-1196508934=:96939 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Hi All; I am a new in computational chemistry field. Now, I am reading about the basis sets. There are something confused me and would be appreciative if anyone helps me to correct my erroneous concepts. Suppose that we have a compound containing carbons with sp2 and sp3 hybridization, for example CH3CH=CH2, and the basis set is 6-31G. Now my question is: 6-31G basis set for Csp3 is similar to 6-31G basis set for Csp2. Is this right??!! Please correct my concept. Thanks a Lot --------------------------------- Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try it now. --0-951450408-1196508934=:96939 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit
Hi All;
I am a new in computational chemistry field. Now, I am reading about the basis sets. There are something confused me and would be appreciative if anyone helps me to correct my erroneous concepts.
Suppose that we have a compound containing carbons with sp2 and sp3 hybridization, for example CH3CH=CH2, and the basis set is 6-31G. Now my question is: 6-31G basis set for Csp3 is similar to 6-31G basis set for Csp2. Is this right??!! Please correct my concept.
 
Thanks a Lot
 

Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try it now. --0-951450408-1196508934=:96939-- From owner-chemistry@ccl.net Sat Dec 1 09:46:01 2007 From: "John McKelvey jmmckel _ gmail.com" To: CCL Subject: CCL:G: basis set erroneous concept Message-Id: <-35744-071201091017-2301-9rDjRORZGea7S+n2+5oVKg,+,server.ccl.net> X-Original-From: "John McKelvey" Content-Type: multipart/alternative; boundary="----=_Part_4116_26694201.1196518206247" Date: Sat, 1 Dec 2007 09:10:06 -0500 MIME-Version: 1.0 Sent to CCL by: "John McKelvey" [jmmckel!=!gmail.com] ------=_Part_4116_26694201.1196518206247 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline This is a very good question!! The short answer is that the iterative SCF process, whether Hartree-Fock or DFT, allows the distribution of electrons to be optimal for any local chemical environment. This process has optimal chance of representing the "true chemical picture" the larger the number of mathematical electronic distribution functions, here basis orbitals. Hence, a simple Slater orbital, or its popular Gaussian approximation STO-nG, is at the most restrictive end of the spectrum, while something like 6-311++G** is in the direction of the much more flexible set of distribution functions, but not necessarily _the_ most flexible, but may be close enough for practical application. Now something like 6-31G is in between, among many other possibilities. Which of the intermediate set of functions one chooses is controlled by how well it allows the most suitable results for a given application. There are many papers by the Pople group published during the development of various basis sets, just to mention one of many places to read about this. Hope this helps! Cheers, John McKelvey On Dec 1, 2007 6:35 AM, mohamed aish mhmdaish!^!yahoo.com < owner-chemistry::ccl.net> wrote: > Hi All; > I am a new in computational chemistry field. Now, I am reading about the > basis sets. There are something confused me and would be appreciative if > anyone helps me to correct my erroneous concepts. > Suppose that we have a compound containing carbons with sp2 and sp3hybridization, for example CH > 3CH=CH2, and the basis set is 6-31G. Now my question is: 6-31G basis set > for Csp3 is similar to 6-31G basis set for Csp2. Is this right??!! Please > correct my concept. > > Thanks a Lot > > > ------------------------------ > Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try > it now. ------=_Part_4116_26694201.1196518206247 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline This is a very good question!!

The short answer is that the iterative SCF process, whether Hartree-Fock or DFT,  allows the distribution of electrons to be optimal for any local chemical environment.  This process has optimal chance of representing the "true chemical picture" the larger the number of mathematical electronic distribution functions, here basis orbitals.  Hence, a simple Slater orbital, or its popular Gaussian  approximation STO-nG, is at the most restrictive end of the spectrum, while something like 6-311++G** is in the direction of the much more flexible set of distribution functions, but not necessarily _the_ most flexible, but may be close enough for practical application.  Now something like 6-31G is in between, among many other possibilities.   Which of the intermediate set of functions one chooses is controlled by how well it allows the most suitable results for a given application.

There are many papers by the Pople group published during the development of various basis sets, just to mention one of many places to read about this.

Hope this helps!

Cheers,

John McKelvey

On Dec 1, 2007 6:35 AM, mohamed aish mhmdaish!^!yahoo.com <owner-chemistry::ccl.net> wrote:
Hi All;
I am a new in computational chemistry field. Now, I am reading about the basis sets. There are something confused me and would be appreciative if anyone helps me to correct my erroneous concepts.
Suppose that we have a compound containing carbons with sp2 and sp3 hybridization, for example CH3CH=CH2, and the basis set is 6-31G. Now my question is: 6-31G basis set for Csp3 is similar to 6-31G basis set for Csp2 . Is this right??!! Please correct my concept.
 
Thanks a Lot
 

Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try it now.

------=_Part_4116_26694201.1196518206247-- From owner-chemistry@ccl.net Sat Dec 1 11:56:00 2007 From: "Agesilaos George Hantzis algar7#%#in.gr" To: CCL Subject: CCL:G: Disk limitations in Gaussian 98 Message-Id: <-35745-071201050235-28507-3IkuDb20RQll/kUIW+zODA^-^server.ccl.net> X-Original-From: "Agesilaos George Hantzis" Date: Sat, 1 Dec 2007 05:02:31 -0500 Sent to CCL by: "Agesilaos George Hantzis" [algar7[a]in.gr] Dear gentlemen, i would like to know if anyone has had disk limitation problems when using Gaussian 98 for large jobs (involving large basis sets and post-HF calculations). I am aware that Gaussian allows the user to make up to 8 seagments for the rwf file, up to 2GB each. That makes 16GB total. Is there any way to avoid consuming all the 16GB availabke? Because if all the seagments are filled the job obviously stops. Thank you From owner-chemistry@ccl.net Sat Dec 1 18:33:01 2007 From: "Hod Greeley hod-ccl(0)greeley.org" To: CCL Subject: CCL: basis set erroneous concept Message-Id: <-35746-071201155232-20965-fekAZwaXftnFw1X2fksoHQ,,server.ccl.net> X-Original-From: "Hod Greeley" Content-Transfer-Encoding: 8bit Content-Type: text/plain;charset=iso-8859-1 Date: Sat, 1 Dec 2007 12:42:55 -0800 (PST) MIME-Version: 1.0 Sent to CCL by: "Hod Greeley" [hod-ccl-,-greeley.org] The really short answer is that the 6-31G basis is a set of functions defined totally independently of the orbitals those functions are used to describe. The idea is that within a molecule, the distribution of the electron densities can be approximately described by sums of basis functions. This is just like a Fourier transform. In fact, you could use sines and cosines as the basis functions for a molecular system. However, since sines and cosines do not look very similar to orbitals, you would have to include many, many terms in a (truncated Fourier) sum before your error (in neglecting the rest of the infinite number of terms) became small. This is theoretically fine, but impractical for actual computation. So, instead, comp. chemists choose other functions which more closely resemble orbitals. This way you only need a few functions to achieve a good approximation. Usually, you pick one defined set of functions for any one calculation, i.e. a basis set. So, yes, in your example you would use the 6-31G basis set functions in sums to approximate both sp2 and sp3 orbitals. Or, you might choose 6-31G**, which includes more functions. This means you would most likely get a more accurate answer, but at the expense of the calculations taking longer. I hope that helps. Best, Hod Greeley > Hi All; > I am a new in computational chemistry field. Now, I am reading about the > basis sets. There are something confused me and would be appreciative if > anyone helps me to correct my erroneous concepts. > Suppose that we have a compound containing carbons with sp2 and sp3 > hybridization, for example CH3CH=CH2, and the basis set is 6-31G. Now my > question is: 6-31G basis set for Csp3 is similar to 6-31G basis set for > Csp2. Is this right??!! Please correct my concept. > > Thanks a Lot > > > > --------------------------------- > Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try > it now.