From owner-chemistry@ccl.net Thu Sep 13 01:24:00 2012 From: "Ronald Cook cookrl^tda.com" To: CCL Subject: CCL: regarding negative fukui function Message-Id: <-47579-120911233749-10702-4Tp7HZ5ilwgcBnFeeMA/3g- -server.ccl.net> X-Original-From: Ronald Cook Content-Type: multipart/alternative; boundary=f46d0447f2ced140c904c978e926 Date: Tue, 11 Sep 2012 21:37:42 -0600 MIME-Version: 1.0 Sent to CCL by: Ronald Cook [cookrl:+:tda.com] --f46d0447f2ced140c904c978e926 Content-Type: text/plain; charset=ISO-8859-1 Ambrish Most likely your problem is the use of the Mullikin charges. They give unrealistic and incorrect values for charges.Take a look at Condensation of Frontier Molecular Orbital Fukui Functions by Bulat et al. J. Phys. Chem. A 2004, 108, 342-349 aper "Possible negative values for the Fukui indexes have been discussed in the literature and considered as artifacts coming > from the condensation procedure12 or due to strong structural distortions14 (see also refs 13 and 15-17). Thanikaivelan et al.18 have thoroughly studied the effects of the population scheme and the basis set dependency of the Fukui indexes within the finite difference approximation eqs 9-11. *The most stable schemes upon basis set modification turn out to be the Atoms in Molecules (AIM)19 and the CHELPG (charges from electrostatic potentials, using a grid-based method),*20 this last one being based on the molecular electrostatic potential (MESP) to derive the atomic charges. Interestingly enough, these two schemes provide also very similar Fukui indexes and they both predict appropriate reactivity sites for all kinds of attacks (nucleophilic, electrophilic, and radical). Although they note that Hirshfeld partitioning provides in all studied cases nonnegative Fukui indexes, as also stated by Roy et al.,12 this fact cannot be generally extended since the allowance of negative values is in part a consequence of the finite difference approximation. Indeed, eqs 3-5 might be negative at some points since FN+1(r) might be smaller than FN(r) and FN(r) might be smaller than FN-1(r). Hence, regardless of the condensation scheme chosen negative Fukui indexes might appear. Furthermore, Hirshfeld partitioning fails to predict the correct reactivity trends in some cases.12,18" and their references On Tue, Sep 11, 2012 at 11:39 AM, AMBRISH KUMAR SRIVASTAVA ambrishphysics]^[ gmail.com wrote: > > Sent to CCL by: "AMBRISH KUMAR SRIVASTAVA" [ambrishphysics_._gmail.com] > Respected all, > During calculation on fukui fn using mullikan atomic charges, i got a > number of negative values for e.g. f0 values are given below: > -0.82305 > -0.90080 > 0.22285 > -0.14005 > 0.32460 > -0.12940 > 0.58775 > -0.13240 > -0.45095 > -0.12075 > 0.95505 > -0.12835 > -0.13485 > 0.36405 > -0.03600 > -0.24670 > -0.15305 > -0.05770 > how to interpret these values?? how can i extract any useful info with > this data set?? > any kind of help will be highly appreciated! > thanking you in advance.. > Ambrish K. Srivastava > ambrishphysics]~[gmail.com> > > -- Ronald L Cook Principal Scientist TDA Research, Inc. cookrl[A]tda.com 303-940-2302 --f46d0447f2ced140c904c978e926 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Ambrish

Most likely your problem is the use of the Mullikin charges.= =A0 They give unrealistic and incorrect values for charges.Take a look at <= br>
Condensation of Frontier Molecular Orbital Fukui Functions by Bulat = et al. J. Phys. Chem. A 2004, 108, 342-349
aper

"Possible negative values for the Fukui indexes have been<= br>discussed in the literature and considered as artifacts coming
from t= he condensation procedure12 or due to strong structural
distortions14 (s= ee also refs 13 and 15-17).
Thanikaivelan et al.18 have thoroughly studied the effects of
the popula= tion scheme and the basis set dependency of the Fukui
indexes within the= finite difference approximation eqs 9-11.
The most stable schemes up= on basis set modification turn out
to be the Atoms in Molecules (AIM)19 and the CHELPG
(charges from electr= ostatic potentials, using a grid-based
method),20 this last one bein= g based on the molecular electrostatic
potential (MESP) to derive the at= omic charges. Interestingly
enough, these two schemes provide also very similar Fukui
indexes and th= ey both predict appropriate reactivity sites for
all kinds of attacks (n= ucleophilic, electrophilic, and radical).
Although they note that Hirshf= eld partitioning provides in all
studied cases nonnegative Fukui indexes, as also stated by Roy
et al.,12= this fact cannot be generally extended since the
allowance of negative = values is in part a consequence of the
finite difference approximation. = Indeed, eqs 3-5 might be
negative at some points since FN+1(r) might be smaller than
FN(r) and FN= (r) might be smaller than FN-1(r). Hence, regardless
of the condensation= scheme chosen negative Fukui indexes
might appear. Furthermore, Hirshfe= ld partitioning fails to predict
the correct reactivity trends in some cases.12,18"

and their re= ferences

On Tue, Sep 11, 2012 at 11:39 AM= , AMBRISH KUMAR SRIVASTAVA ambrishphysics]^[gm= ail.com <owner-chemistry[A]ccl.net> wrote:

Sent to CCL by: "AMBRISH KUMAR SRIVASTAVA" [ambrishphysics_._gmail.com]
Respected all,
During calculation on fukui fn using mullikan atomic charges, i got a numbe= r of negative values for e.g. f0 values are given below:
-0.82305
-0.90080
=A00.22285
-0.14005
=A00.32460
-0.12940
=A00.58775
-0.13240
-0.45095
-0.12075
=A00.95505
-0.12835
-0.13485
=A00.36405
-0.03600
-0.24670
-0.15305
-0.05770
how to interpret these values?? how can i extract any useful info with this= data set??
any kind of help will be highly appreciated!
thanking you in advance..
Ambrish K. Srivastava
ambrishphysics]~[gmail.com



-=3D This is automatically added to each message by the mailing script =3D-=
E-mail to subscribers: CHEMISTRY[A]ccl.n= et or use:
=A0 =A0 =A0 http://www.ccl.net/cgi-bin/ccl/send_ccl_message

E-mail to administrators: CHEM= ISTRY-REQUEST[A]ccl.net or use
=A0 =A0 =A0 http://www.ccl.net/cgi-bin/ccl/send_ccl_message

Subscribe/Unsubscribe:
=A0 =A0 =A0 http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.n= et/jobs
Conferences: http://server.ccl.net/chemistry/announcements/co= nferences/

Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml
=A0 =A0 =A0 h= ttp://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/





--
Ronald L Cook
Princi= pal Scientist
TDA Research, Inc.
cookrl[A]tda.com
303-940-2302

--f46d0447f2ced140c904c978e926--