From owner-chemistry@ccl.net Thu May 16 12:09:01 2013 From: "Scott McKechnie jsm78/./cam.ac.uk" To: CCL Subject: CCL:G: Orbital energies for neutral and cation species in vacuum and solution Message-Id: <-48704-130516120540-21745-Cdc6lyqnvY5oFsiz1Xy4Wg*server.ccl.net> X-Original-From: Scott McKechnie Content-Type: multipart/alternative; boundary=001a11c2ce1607d0ff04dcd809f1 Date: Thu, 16 May 2013 17:05:29 +0100 MIME-Version: 1.0 Sent to CCL by: Scott McKechnie [jsm78 ~~ cam.ac.uk] --001a11c2ce1607d0ff04dcd809f1 Content-Type: text/plain; charset=ISO-8859-1 Hi Johannes, Many thanks for your reply and sorry to drag this discussion on but would the above comments change for quite simple systems? For instance, my main concern is about the calculations of delta SCF (vertical and adiabatic) values for organic dye molecules. I'm guessing a benchmark study would be advisable to investigate the sensitivity? Best wishes, Scott On 16 May 2013 14:06, Johannes Hachmann jh=chemistry.harvard.edu < owner-chemistry * ccl.net> wrote: > > Sent to CCL by: "Johannes Hachmann" [jh^-^chemistry.harvard.edu] > Hi Scott, > > The decision between U and RO is tricky and in my opinion there is no > golden > bullet - both approaches have their problems :). The U results may not give > you a good quantum state, in particular if you have excessive spin > contamination, while RO is not very flexible and does not allow for DODS, > i.e., the R part cannot adequately account for the interactions with the > unpaired electron. In my experience, U results tend to be better, but one > has to be more careful how to interpret them. If you have very large spin > polarization this indicates that your electronic structure is too > complicated for a single-reference approach and you may want to try > something more sophisticated than DFT. All bets are off then for the DFT > results: you know that RO will be bad, while U results *may* still be ok > (but somewhat artificially so). > > If you use U for the cation, you should try using U for the neutral > molecule > as well (don't forget to break spin symmetry in your guess!). If the > molecule is complicated and the neutral one already shows spin > polarization, > you *may* get some error cancellation, since both species are treated on > the > same footing. I would then also use U for the respective geometry > optimizations. > > Hope this helps > > Best > > Johannes > > ----------------------------------------------- > Dr. Johannes Hachmann > Research Associate > Harvard University > Department of Chemistry and Chemical Biology > 12 Oxford St, Rm M104A > Cambridge, MA 02138 > ----------------------------------------------- > > > > -----Original Message----- > > From: owner-chemistry+jh==chemistry.harvard.edu..ccl.net [mailto:owner- > > chemistry+jh==chemistry.harvard.edu..ccl.net] On Behalf Of Scott > McKechnie > > jsm78]![cam.ac.uk > > Sent: Thursday, 16 May, 2013 07:28 > > To: Hachmann, Johannes > > Subject: CCL:G: Orbital energies for neutral and cation species in vacuum > and > > solution > > > > Dear Dr. Hachmann and Dr. Kumar, > > > > > > Many thanks for your very helpful replies and for the excellent > references. > > > > > Did you set up your delta-SCF as restricted open shell or > unrestricted? > > > > I used the default settings in Gaussian09 which is unrestricted for the > cation, > > but I would appreciate any advise here. I notice that the delta SCF > values > only > > differ by 0.07 eV but the orbital energies are significantly different > (cation gas > > phase alpha HOMO and LUMO values of -6.48 eV and -6.36 eV as compared > > with the unrestricted beta gas phase HOMO and LUMO values of -10.65 eV > and > > -8.76 eV). > > > > > > I had two follow up questions here. > > > > > > 1. Using ROB3LYP results in degenerate alpha and beta orbitals? > > > > > > 2. Is it advised to do cation optimization with UB3LYP instead of B3LYP? > > > > > > Thanks again and very best wishes, > > > > Scott > > > > > > > > > > On 15 May 2013 04:30, Ramesh Kumar rameshchitumalla^gmail.com > chemistry,+,ccl.net> wrote: > > > > > > > > Sent to CCL by: Ramesh Kumar [rameshchitumalla(a)gmail.com] > > Dear Scott, > > > > The reply from Dr. Johannes Hachmann is really very useful. > > The orbital energy of a cation is much lower than that of its > > corresponding neutral molecule and again it comes very near to the > > case similar to neutral molecule in the presence of a polar > solvent. > > For some numbers you can see CPL 396 (2004) 43-48. > > > > > > > > -- > > With Best Regards: > > > > CH. Ramesh Kumar > > Senior Research Fellow, > > Computational Chemistry Lab, > > Indian Institute of Chemical Technology(IICT), > > Tarnaka, > > Hyderabad.> > > > > > > E-mail to subscribers: CHEMISTRY,+,ccl.net or use:> > > E-mail to administrators: CHEMISTRY-REQUEST,+,ccl.net or use> > Conferences: > > http://server.ccl.net/chemistry/announcements/conferences/> > > > --001a11c2ce1607d0ff04dcd809f1 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Hi Johannes,

Many thanks for your r= eply and sorry to drag this discussion on but would the above comments chan= ge for quite simple systems? For instance, my main concern is about the cal= culations of delta SCF (vertical and adiabatic) values for organic dye mole= cules. I'm guessing a benchmark study would be advisable to investigate= the sensitivity?

Best wishes,

Scott
=A0 =A0


On 16 May 2013 14:06= , Johannes Hachmann jh=3Dchemistry= .harvard.edu <owner-chemistry * ccl.net> wrote:

Sent to CCL by: "Johannes Hachmann" [jh^-^chemistry.harvard.edu]
Hi Scott,

The decision between U and RO is tricky and in my opinion there is no golde= n
bullet - both approaches have their problems :). The U results may not give=
you a good quantum state, in particular if you have excessive spin
contamination, while RO is not very flexible and does not allow for DODS, i.e., the R part cannot adequately account for the interactions with the unpaired electron. In my experience, U results tend to be better, but one has to be more careful how to interpret them. If you have very large spin polarization this indicates that your electronic structure is too
complicated for a single-reference approach and you may want to try
something more sophisticated than DFT. All bets are off then for the DFT results: you know that RO will be bad, while U results *may* still be ok (but somewhat artificially so).

If you use U for the cation, you should try using U for the neutral molecul= e
as well (don't forget to break spin symmetry in your guess!). If the molecule is complicated and the neutral one already shows spin polarization= ,
you *may* get some error cancellation, since both species are treated on th= e
same footing. I would then also use U for the respective geometry
optimizations.

Hope this helps

Best

Johannes

-----------------------------------------------
Dr. Johannes Hachmann
Research Associate
Harvard University
Department of Chemistry and Chemical Biology
12 Oxford St, Rm M104A
Cambridge, MA 02138
-----------------------------------------------


> -----Original Message-----
> From: owner-chemistry+jh=3D=3Dchemistry.harvard.edu..cc= l.net [mailto:owner-
> chemistry+jh=3D=3Dchemistry.h= arvard.edu..ccl.net] O= n Behalf Of Scott McKechnie
> jsm78]![cam.ac.uk > Sent: Thursday, 16 May, 2013 07:28
> To: Hachmann, Johannes
> Subject: CCL:G: Orbital energies for neutral and cation species in vac= uum
and
> solution
>
> Dear Dr. Hachmann and Dr. Kumar,
>
>
> Many thanks for your very helpful replies and for the excellent
references.
>
> > =A0Did you set up your delta-SCF as restricted open shell or unre= stricted?
>
> I used the default settings in Gaussian09 which is unrestricted for th= e
cation,
> but I would appreciate any advise here. I notice that the delta SCF va= lues
only
> differ by 0.07 eV but the orbital energies are significantly different=
(cation gas
> phase alpha HOMO and LUMO values of -6.48 eV and -6.36 eV as compared<= br> > with the unrestricted beta gas phase HOMO and LUMO values of -10.65 eV= and
> -8.76 eV).
>
>
> I had two follow up questions here.
>
>
> 1. Using ROB3LYP results in degenerate alpha and beta orbitals?
>
>
> 2. Is it advised to do cation optimization with UB3LYP instead of B3LY= P?
>
>
> Thanks again and very best wishes,
>
> Scott
>
>
>
>
> On 15 May 2013 04:30, Ramesh Kumar rameshchitumalla^gmail.com <owner-
> chemistry,+,ccl.net&g= t; wrote:
>
>
>
> =A0 =A0 =A0 Sent to CCL by: Ramesh Kumar [rameshchitumalla(a)gmail.com]
> =A0 =A0 =A0 Dear Scott,
>
> =A0 =A0 =A0 The reply from Dr. Johannes Hachmann is really very useful= .
> =A0 =A0 =A0 The orbital energy of a cation is much lower than that of = its
> =A0 =A0 =A0 corresponding neutral molecule and again it comes =A0very = near to the
> =A0 =A0 =A0 case similar to neutral molecule in the presence of a pola= r solvent.
> =A0 =A0 =A0 For some numbers you can see CPL 396 (2004) 43-48.
>
>
>
> =A0 =A0 =A0 --
> =A0 =A0 =A0 With Best Regards:
>
> =A0 =A0 =A0 CH. Ramesh Kumar
> =A0 =A0 =A0 Senior Research Fellow,
> =A0 =A0 =A0 Computational Chemistry Lab,
> =A0 =A0 =A0 Indian Institute of Chemical Technology(IICT),
> =A0 =A0 =A0 Tarnaka,
> =A0 =A0 =A0 Hyderabad.>
>
>
> =A0 =A0 =A0 E-mail to subscribers: CHEMI= STRY,+,ccl.net or use:>=
> =A0 =A0 =A0 E-mail to administrators: CHEMISTRY-REQUEST,+,ccl.net or use> =A0 Conferenc= es:
> http://server.ccl.net/chemistry/announcements/conference= s/>
>
>
>
>



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