From owner-chemistry@ccl.net Sun Sep 10 16:36:00 2017 From: "Henrique C. S. Junior henriquecsj|,|gmail.com" To: CCL Subject: CCL: Correctly evaluating spin states of a cobalt trimer (using Single Points)? Message-Id: <-52991-170910160343-26337-RliFQ4ND2HEr5umZAMOCFA**server.ccl.net> X-Original-From: "Henrique C. S. Junior" Content-Type: multipart/alternative; boundary="001a113ff1924124720558db4eca" Date: Sun, 10 Sep 2017 17:02:56 -0300 MIME-Version: 1.0 Sent to CCL by: "Henrique C. S. Junior" [henriquecsj=-=gmail.com] --001a113ff1924124720558db4eca Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Dear Professor Neese, thank you for your kind reply and pointing me to your review; that was really helpful. All the best. On Sun, Sep 10, 2017 at 1:43 PM, Neese, Frank frank.neese * cec.mpg.de < owner-chemistry^ccl.net> wrote: > Dear Henrique, > > This is the kind of problem where you have to pay attention to the actual > electronic structure and not just run calculations. > > You have to pay attention to spin coupling. Co(III) is d6 system. > Depending on the coordination environment, the most likely local spin > states are Sl=3D0 or 1. The three local spins - if there are any - could > couple to St=3D3,2,1 or perhaps 0. In a triangle spin frustration occurs = and > the coupling is most likely antiferromagnetic which would leave St=3D1 mo= st > likely (if Sl=3D1), but it could well be more complicated if there is any > orbital degeneracy. > > The point is that the lower spin states are not single determinants and > hence just entering a given multiplicity in a DFT program and run with it > is incorrect. You obtain broken symmetry determinants that are > eigenfunctions to Sz but not S**2. Spin projection techniques must then b= e > applied to estimate spin state energies. > > A multireference method is an alternative, but you have to work hard to > overcome the self consistent field bias for high spin states and the > underestimation of exchange coupling. > > IMHO these problems are most easily solved experimentally. Connecting to = the > experiment (susceptibility, MCD, EPR ...) is vital in the first place. > > Please allow me - My coordination chemistry reviews article from 2009 > provides a somewhat detailed discussion. From a more conceptual point of > view you may want to check a just published Angewandte Chemie Essay. A > whole issue of coordination chemistry rev has recently been devoted to > molecular magnetism - there generally is a rich literature on this type = of > problem. > > Good luck, > Cheers, > Frank > > Von meinem iPhone gesendet > > Am 10.09.2017 um 18:15 schrieb Sergio Emanuel Galembeck segalemb]-[usp.br > : > > Dear Henrique, > > I suggest that for each spin state you optimize the geometry. Some of thi= s > states could generate an unstable geometry. > > Best regards, > > Sergio > > Prof. Sergio Emanuel Galembeck > Computational Quantum Chemistry Laboratory > Departamento de Qu=C3=ADmica - FFCLRP-USP > Av. Bandeirantes, 3900 > > 14040-901 - Ribeirao Preto-SP > Brasil > > phone: +55(16)33153765 <(16)%203315-3765> > segalemb~!~usp.br > > 2017-09-10 9:03 GMT-03:00 Henrique C. S. Junior henriquecsj+/-gmail.com < > owner-chemistry~!~ccl.net>: > >> Dear colleagues, I=E2=80=99m working with a Cobalt(II) trimer whose mole= cular >> structure was achieved by Single Crystal X-Ray Diffraction. My task now = is >> to check the spin states of the structure (High or Low spin). Since Co(I= I) >> can have 1 or 3 unpaired electrons, I=E2=80=99m approaching this problem= by >> calculating Single Points for every possible multiplicity (10, 8, 6, 4, = 2) >> and assuming that the most stable is the one that represents my structur= e >> (and my spin states). >> >> Is this approach correct? >> >> Thank you >> >> -- >> *Henrique C. S. Junior* >> >> > --=20 *Henrique C. S. Junior* --001a113ff1924124720558db4eca Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Dear Professor Neese, thank you for your kind reply and pointi= ng me to your review; that was really helpful.

All the best.

On Sun, Sep 10, 201= 7 at 1:43 PM, Neese, Frank frank.neese * cec.= mpg.de <owner-chemistry^ccl.net> wrote:
Dear Henrique,

This is the kind = of problem where you have to pay attention to the actual electronic structu= re and not just run calculations.

You have to pay attention to spin coupling. C= o(III) is d6 system. Depending on the coordination environment, the most li= kely local spin states are Sl=3D0 or 1. The three local spins - if there are any - could couple to St=3D3,2,1 or perhaps 0. In a t= riangle spin frustration occurs and the coupling is most likely antiferroma= gnetic which would leave St=3D1 most likely (if Sl=3D1), but it could well = be more complicated if there is any orbital degeneracy.

The point is that the lower spin states are n= ot single determinants and hence just entering a given multiplicity in a DF= T program and run with it is incorrect. You obtain broken symmetry determinants that are eigenfunctions to Sz but not S**2. Spin pro= jection techniques must then be applied to estimate spin state energies.=C2= =A0

A multireference method is an alternative, bu= t you have to work hard to overcome the self consistent field bias for high= spin states and the underestimation of exchange coupling.

IMHO these problems are most easily solved ex= perimentally. Connecting to=C2=A0the experiment=C2=A0(susceptibility, MCD, EPR ...) is vital in the first p= lace.

Please allow me - My coordination chemistry r= eviews article from 2009 provides a somewhat detailed discussion. From a mo= re conceptual point of view you may want to check a just published Angewandte Chemie Essay. A whole issue of coordination chem= istry rev has recently been devoted to molecular magnetism - there generall= y =C2=A0is a rich literature on this type of problem.

Good luck,
Cheers,
Frank

Von meinem iPhone gesendet

Am 10.09.2017 um 18:15 schrieb Sergio Emanuel Galembeck segalemb]-[usp.br <owner-chemistry(~)ccl.net>:<= br>
Dear Henrique,

I suggest that for each spin state you optimize the geometry. Some of = this states could generate an unstable geometry.=C2=A0

Best regards,

Sergio

Prof. Sergio Emanuel Galembeck
Computational Quantum Chemistry Laboratory
Departamento de Qu=C3=ADmica - FFCLRP-USP
14040-901 - Ribeirao Preto-SP
Brasil


2017-09-10 9:03 GMT-03:00 Henrique C. S. Junior = henriquecsj+/-gmail.com <owner-chemistry~!~ccl.net>:

Dear colleagues, I=E2=80=99m working with a Cobalt(II)= trimer whose molecular structure was achieved by Single Crystal X-Ray Diff= raction. My task now is to check the spin states of the structure (High or = Low spin). Since Co(II) can have 1 or 3 unpaired electrons, I=E2=80=99m approaching this problem by calculating Single Poin= ts for every possible multiplicity (10, 8, 6, 4, 2) and assuming that the m= ost stable is the one that represents my structure (and my spin states).

Is this approach correct?

Thank you


--
Henrique C. S. Junior





--
Henri= que C. S. Junior

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