From owner-chemistry@ccl.net Sat Jun 11 17:57:01 2016 From: "Henrique C. S. Junior henriquecsj-x-gmail.com" To: CCL Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons means a smaller coupling? Message-Id: <-52238-160611175500-8243-OGDGSKKcIpSCtYCmtkNWFA++server.ccl.net> X-Original-From: "Henrique C. S. Junior" Content-Type: multipart/alternative; boundary=001a113ce462aaa4af053507b415 Date: Sat, 11 Jun 2016 18:54:15 -0300 MIME-Version: 1.0 Sent to CCL by: "Henrique C. S. Junior" [henriquecsj-,-gmail.com] --001a113ce462aaa4af053507b415 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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 increase in magnetic coupling)? --=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 --001a113ce462aaa4af053507b415 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

= I hope this is not a "homework&quo= t; question, but I'm having a bad time trying to figure this out.

Ava= ilable literature proposes 3 equations to calculate the coupling constant d= uring a Broken-Symmetry approach:

=

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

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)?

=

--

<= span style=3D"color:rgb(139,139,139)"><= b>Henrique C. S. Junior
Qu=C3=ADmico = Industrial - UFRRJ

Mestrando em Qu=C3= =ADmica Inorg=C3=A2nica - UFRRJ
Centro de Processamento de Dados - PMP

--001a113ce462aaa4af053507b415-- From owner-chemistry@ccl.net Sat Jun 11 21:54:00 2016 From: "Rodriguez, Jorge H jhrodrig()purdue.edu" To: CCL Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons means a smaller coupling? Message-Id: <-52239-160611215157-23168-wwlhmYQsWxauwntyging6Q**server.ccl.net> X-Original-From: "Rodriguez, Jorge H" Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_146569630790633172purdueedu_" Date: Sun, 12 Jun 2016 01:51:50 +0000 MIME-Version: 1.0 Sent to CCL by: "Rodriguez, Jorge H" [jhrodrig|a|purdue.edu] --_000_146569630790633172purdueedu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Dear Henrique: The magnitude and sign of the Heisenberg exchange constant (J) is a fairly = complex function of, among several other factors, geometric structure, type of bridging ligands, spin densities/magnetic mome= nts of the constituent spin centers, fairly localized (e.g. metal atoms) or delocalized (e.g. small radical molecules) nature of= the spin centers, etc. For a comprehensive discussion of the origin, magnitude and computation of= the exchange constant, within a spin-polarized DFT approach, please see: "Density Functional Theory of Spin-Coupled Models for Diiron-Oxo Proteins: Effects of Oxo and Hydroxo Bridging on Geometry, Electronic Structure and M= agnetism"., J.H. Rodr=EDguez and J.K. McCusker., J. Chem. Phys. 116, 6253-6270 (2002). Best Wishes, Prof. Jorge H. Rodriguez ____________________________________________________ Computational Biomolecular & Mesoscopic Physics Group Purdue University West Lafayette, IN 47907, USA https://www.physics.purdue.edu/biomolecular_physics/index.html ________________________________ > From: owner-chemistry+jhrodrig=3D=3Dpurdue.edu:ccl.net on behalf of Henrique C. S. Junior henriquec= sj-x-gmail.com Sent: Saturday, June 11, 2016 5:54 PM To: Rodriguez, Jorge H Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons means a= smaller coupling? 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 constan= t 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 hav= e unpaired electrons, the minor will be Jab. Why does this happen? Doesn't = more unpaired electrons increase magnetic momenta (and an increase in magne= tic coupling)? -- Henrique C. S. Junior Qu=EDmico Industrial - UFRRJ Mestrando em Qu=EDmica Inorg=E2nica - UFRRJ Centro de Processamento de Dados - PMP --_000_146569630790633172purdueedu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Dear Henrique:

The magnitude and sign of the Heisenberg exchange constant (J) is a= fairly complex function of, among several other factors,

geometric structure, type of bridging ligands, spin densities/magne= tic moments of the constituent spin centers, fairly localiz= ed

(e.g. metal atoms) or deloca= lized (e.g. small radical mole= cules) nature of the spin centers, etc.

For a comprehensive discussion of the origin, magnitude and computat= ion of the exchange constant, within a spin-polarized DFT approach,&nb= sp;please see:

&quo= t;Density Functional Theory of Spin-Coupled Models for Diiron-Oxo Proteins:

Effe= cts of Oxo and Hydroxo Bridging on Geometry, Electronic Structure and Magnetism".,

J.H.= Rodr=EDguez and J.K. McCusker., J. Chem. Phys. 116, 6253-6270 (2002).

Best= Wishes,

Prof= . Jorge H. Rodriguez

____= ________________________________________________

Computational Biomolecular & Mesoscopic Physics Group

Purdue University

West Lafayette, IN 47907, USA

https://www.physics.purdue.edu/bi= omolecular_physics/index.html

From: owner-chemistry+j= hrodrig=3D=3Dpurdue.edu:ccl.net <owner-chemistry+jhrodrig=3D=3Dpurdu= e.edu:ccl.net> on behalf of Henrique C. S. Junior henriquecsj-x-gmail.co= m <owner-chemistry:ccl.net>
Sent: Saturday, June 11, 2016 5:54 PM
To: Rodriguez, Jorge H
Subject: CCL: Coupling constant (Jab) - Why more unpaired electrons = means a smaller coupling?

I hope thi= s 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 intrig= ued 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 unpai= red electrons increase magnetic momenta (and an increase in magnetic coupling)?

--

Henrique C. S. Junior
Qu=EDmico Industrial - UFRRJ

Mestrando em Qu=EDmica Inorg=E2nica - UFRRJ
Centro de Processamento de Dados - PMP

--_000_146569630790633172purdueedu_--