From owner-chemistry@ccl.net Wed Jun 29 08:10:01 2016 From: "Henrique C. S. Junior henriquecsj~~gmail.com" To: CCL Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons means a smaller coupling? Message-Id: <-52260-160629070157-8778-DBsI8WNQQN3+DfoQ711M8A{=}server.ccl.net> X-Original-From: "Henrique C. S. Junior" Content-Type: multipart/alternative; boundary=001a113dd29432bd3c053668ae65 Date: Wed, 29 Jun 2016 08:01:11 -0300 MIME-Version: 1.0 Sent to CCL by: "Henrique C. S. Junior" [henriquecsj+*+gmail.com] --001a113dd29432bd3c053668ae65 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi, Swetanshu, You don't need the coupling constants before, but you need to perform a study to understand what couplings are relevant to your system (to figure out how complex the Hamiltonian will be). After you understood your system, you can use, as an example, the software DAVE[1] to see if your model fits your experimental data. If not, you have to re-think your system and try again to obtain a better fit. [1] - https://www.ncnr.nist.gov/dave/download.html 2016-06-28 16:53 GMT-03:00 Tandon Swetanshu tandons-,-tcd.ie < owner-chemistry.:.ccl.net>: > Hi Henrique, > > Thanks a lot for the insight. I have a small doubt. Before obtaining the > susceptibility curve, we need to obtain the coupling constant. So can't w= e > just compare the calculated coupling constants with the experimental ones= ? > > Thanks again, > Swetanshu. > > On 26 June 2016 at 22:05, Henrique C. S. Junior henriquecsj(~)gmail.com < > owner-chemistry!!ccl.net> wrote: > >> Hi, Swetanshu, >> It is not an easy task to decide what configuration is correct to >> describe the magnetic couplings in a polynuclear system. The best approa= ch >> is to compare the various solutions with an experimental magnetic >> susceptibility curve using a statistical fit software (like origin). >> >> >> >> ---------- >> *Henrique C. S. Junior* >> Qu=C3=ADmico Industrial - UFRRJ >> Mestrando em Qu=C3=ADmica Inorg=C3=A2nica - UFRRJ >> Centro de Processamento de Dados - PMP >> >> >> ------------------------------ >> > From: owner-chemistry=C3=8Cl.net >> To: henriquecsjgmail.com >> Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons mean= s >> a smaller coupling? >> Date: Fri, 24 Jun 2016 11:45:36 +0100 >> >> Hi All, >> >> I have a question somewhat related to this topic. When working out the J >> values in a system with more than 3 metal atoms, there are many differen= t >> solutions. Each solutions is obtained by choosing a different set of >> equations. From the above discussion it seems to me that the large >> differeence in the solutions are due to the large number of unpaired >> electrons and the reduction in the spacing between levels at higher ener= gy. >> Due to this, depending upon the states under consideration the J values >> obtained would differ (please correct me if I am wrong). But how does on= e >> decide as to which set of solution is appropriate. >> >> Thanks, >> Swetanshu. >> >> On 12 June 2016 at 00:27, James Buchwald buchwja/rpi.edu < >> owner-chemistry,ccl.net> wrote: >> >> Hi Henrique, >> >> The diminishing Jab that you're predicting assumes that (E[HS] - E[BS]) >> does not grow as quickly as the spin term in the denominator. Depending= on >> the system, this is not necessarily the case, and the energy spacing can >> grow faster. >> >> The reason that the equations appear to cause this is that the >> Heisenberg-Dirac-van Vleck Hamiltonian (which the three equations were >> derived from) has a "spin ladder" of solutions ranging from the low-spin= to >> the high-spin states. If your low-spin state is a singlet, you'll also >> have triplets, pentets, and so on until you reach the high-spin state. >> Similarly, if you start from a doublet, you'll have intermediate quartet= s, >> etc. >> >> As you introduce more and more unpaired electrons, the spin of the >> high-spin state increases - but all of the intermediate states between t= he >> high-spin and low-spin limits still exist. You can work out the splitti= ng >> between these individual states in terms of J, and what ends up happenin= g >> is that the states spread out. The denominator essentially corrects for >> that spacing, rather than saying anything about the strength of the >> magnetic coupling. >> >> Best, >> James >> >> On 06/11/2016 05:54 PM, Henrique C. S. Junior henriquecsj-x-gmail.com >> wrote: >> >> I hope this is not a "homework" question, but I'm having a bad time >> trying to figure this out. >> Available literature proposes 3 equations to calculate the coupling >> constant during a Broken-Symmetry approach: >> >> J(1) =3D -(E[HS]-E[BS])/Smax**2 >> J(2) =3D -(E[HS]-E[BS])/(Smax*(Smax+1)) >> J(3) =3D -(E[HS]-E[BS])/(HS-BS) >> >> I'm intrigued by the fact that, from the equations, the more the system >> have unpaired electrons, the minor will be Jab. Why does this happen? >> Doesn't more unpaired electrons increase magnetic momenta (and an increa= se >> in magnetic coupling)? >> >> -- >> *Henrique C. S. Junior* >> Qu=C3=ADmico Industrial - UFRRJ >> Mestrando em Qu=C3=ADmica Inorg=C3=A2nica - UFRRJ >> Centro de Processamento de Dados - PMP >> >> >> -- >> James R. Buchwald >> Doctoral Candidate, Theoretical Chemistry >> Dinolfo Laboratory >> Dept. of Chemistry and Chemical Biology >> Rensselaer Polytechnic Institutehttp://www.rpi.edu/~buchwj >> >> >> > --=20 *Henrique C. S. Junior* Qu=C3=ADmico Industrial - UFRRJ Mestrando em Qu=C3=ADmica Inorg=C3=A2nica - UFRRJ Centro de Processamento de Dados - PMP --001a113dd29432bd3c053668ae65 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi,=C2=A0Swetanshu,
You don't need the coupling constants before, but you ne= ed to perform a study to understand what couplings are relevant to your sys= tem (to figure out how complex the Hamiltonian will be). After you understo= od your system, you can use, as an example, the software DAVE[1] to see if = your model fits your experimental data. If not, you have to re-think your s= ystem and try again to obtain a better fit.

[1]= -=C2=A0https://www.ncnr.nist.gov/dave/download.html<= /a>

2016-06-28 16:53 GMT-03:00 Tandon Swetanshu tandons-,-tcd.ie <owner-chemistry.:.ccl.net>:
Hi Henrique,
Thanks a lot for the insight. I have a small doubt. Before obtai= ning the susceptibility curve, we need to obtain the coupling constant. So = can't we just compare the calculated coupling constants with the experi= mental ones?

Thanks again,
Swetanshu.

On 26 June 2016 at 22:= 05, Henrique C. S. Junior henriquecsj(~)gmail.com <owner-chemistry!!ccl.net> = wrote:
Hi, S= wetanshu,
It is not an easy task to d= ecide what configuration is correct to describe the magnetic couplings in a= polynuclear system. The best approach is to compare the various solutions = with an experimental magnetic susceptibility curve using a statistical fit = software (like origin).



-= ---------
Henri= que C. S. Junior
Qu=C3=ADmico Industrial - UFRRJ
Mestrando em Qu=C3=ADmica Inorg=C3= =A2nica - UFRRJ
Centro de Processamento de Dados - PMP


= > From: owner-chemistry=C3=8Cl.net
To: henriquecsjgmail.com
Subject: CCL: Coupl= ing constant (Jab) - Why more unpaired electrons means a smaller coupling?<= br>Date: Fri, 24 Jun 2016 11:45:36 +0100

Hi All,
I have a question somewhat related to this topic. When wor= king out the J values in a system with more than 3 metal atoms, there are m= any different solutions.=C2=A0 Each solutions is obtained by choosing a dif= ferent set of equations. From the above discussion it seems to me that the = large differeence in the solutions are due to the large number of unpaired = electrons and the reduction in the spacing between levels at higher energy.= Due to this, depending upon the states under consideration the J values ob= tained would differ (please correct me if I am wrong). But how does one dec= ide as to which set of solution is appropriate.

Thanks,
Swetanshu.

On 12 June 2016 at 00:27= , James Buchwald buchwja/rpi.e= du <owner-chemistry,ccl.net> wrote:
=20 =20 =20
Hi Henrique,

The diminishing Jab that you're predicting assumes that (E[HS] - E[BS]) does not grow as quickly as the spin term in the denominator.=C2=A0 Depending on the system, this is not necessarily the case, and the energy spacing can grow faster.

The reason that the equations appear to cause this is that the Heisenberg-Dirac-van Vleck Hamiltonian (which the three equations were derived from) has a "spin ladder" of solutions ranging f= rom the low-spin to the high-spin states.=C2=A0 If your low-spin state is a singlet, you'll also have triplets, pentets, and so on until you reach the high-spin state.=C2=A0 Similarly, if you start from a doublet= , you'll have intermediate quartets, etc.

As you introduce more and more unpaired electrons, the spin of the high-spin state increases - but all of the intermediate states between the high-spin and low-spin limits still exist.=C2=A0 You can wo= rk out the splitting between these individual states in terms of J, and what ends up happening is that the states spread out.=C2=A0 The denominator essentially corrects for that spacing, rather than saying anything about the strength of the magnetic coupling.

Best,
James

On 06/11/2016 05:54 PM, Henrique C. S. Junior h= enriquecsj-x-gmail.com wrote:
I hope this is not a "homework" question, but I'm= having a bad time trying to figure this out.
Available literature proposes 3 equations to calculate the coupling constant during a Broken-Symmetry approach:

J(1) =3D -(E[HS]-E[BS])/Smax**2
J(2) =3D -(E[HS]-E[BS])/(Smax*(Smax+1))
J(3) =3D -(E[HS]-E[BS])/(<S**2>HS-<S**2>BS)

I'm intrigued by the fact that, from the equations, the more the system have unpaired electrons, the minor will be Jab. Why does this happen? Doesn't more unpaired electrons increase magnetic momenta (and an increase in magnetic coupling)?

--
<= font face=3D"monospace, monospace">Henrique C. S= . Junior
Qu=C3=ADmico Industrial - UFRRJ
<= font face=3D"monospace, monospace">Mestrando em Qu=C3=ADmica Inorg=C3=A2nica - UFRRJ
Centro de Processamento de Dados - PMP

--=20 James R. Buchwald Doctoral Candidate, Theoretical Chemistry Dinolfo Laboratory Dept. of Chemistry and Chemical Biology Rensselaer Polytechnic Institute http://www.rpi.edu= /~buchwj





--
Henriq= ue C. S. Junior
Qu=C3=ADmico Industrial - UFRRJ=
Mestrando em Qu=C3=ADmica Inorg=C3=A2nica - UFRRJCentro de Processamento de Dados - PMP
=
--001a113dd29432bd3c053668ae65--