From owner-chemistry@ccl.net Sun Jul 14 06:32:00 2019 From: "Ulrike Salzner salzner#,#fen.bilkent.edu.tr" To: CCL Subject: CCL: Is the energy of HOMO and LUMO extracted from DFT or TD-DFT calcs? Message-Id: <-53798-190714062558-16754-tO1uibfmg42YkCgHTIIAPw ~~ server.ccl.net> X-Original-From: Ulrike Salzner Content-Type: multipart/alternative; boundary="00000000000026c149058da19153" Date: Sun, 14 Jul 2019 13:25:13 +0300 MIME-Version: 1.0 Sent to CCL by: Ulrike Salzner [salzner*|*fen.bilkent.edu.tr] --00000000000026c149058da19153 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Dear Mo, To compare to redox potentials, you need ionization energies (IPs) electron affinities (EAs), not excitation energies. So TDDFT is not the way to go. Probably adiabatic IPs and EAs are more suitable than vertical ones for comparing with CV data. You can caluclate them with the delta SCF method and you can use the proper solvent which makes a big difference compared to gas phase values. If you use HOMO and LUMO energies to estimate redox potentials you have a couple of issues: 1) It depends on the density functional what values you get. With most functionals negative orbital energies are way off IPs and EAs. You have to use range separated functionals to get reasonable values (Salzner, U.; Baer, R. Koopmans' springs to life. J Chem Phys 2009, 131, 231101). 2) You can not get adiabatic IPs and EAs. I think electrochemistry is rather slow and you should use adiabatic IPs and EAs. 3) You can not include solvent effects because orbital energies do not respond to solvent effects. It is possible to use tuned range separated functionals and to tune them in the presence of solvent, which seems to work (Kronik, L.; K=C3=BCmmel, S. Dielectric Screening Meets Optimally Tune= d Density Functionals. Advanced Materials 2018, 30, 1706560). Therefore, I recommend to use the delta SCF method which gives reasonable results with most density functionals. Best regards, Ulrike Prof. Ulrike Salzner Department of Chemistry Bilkent University 06800 Bilkent, Ankara On Sun, Jul 14, 2019 at 7:34 AM Mo Fateh mo.fateh+*+yahoo.com < owner-chemistry(~)ccl.net> wrote: > > Sent to CCL by: "Mo Fateh" [mo.fateh : yahoo.com] > Dear CCL Members, > > > I am working on the modeling of Organic photovoltaic cell for the first > time. I am confused: > > 1- Is the energy of HOMO and LUMO extracted from DFT (ground state) or TD= - > DFT (vertical excited state) calcs? I want > to compare the HOMO and LUMO energies with those estimated from cyclic > voltametry technique. > > 2- When I should use the energies of HOMO and LUMO of ground state and > when > I should use them in the excited state molecule? > > > > With thanks, > Mo > > > > -=3D This is automatically added to each message by the mailing script = =3D-> > > --00000000000026c149058da19153 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Dear Mo,
To compare to redox potentials, you need ionization en= ergies (IPs) electron affinities (EAs), not excitation energies. So TDDFT i= s not the way to go. Probably adiabatic IPs and EAs are more suitable than = vertical ones for comparing with CV data. You can caluclate them with the d= elta SCF method and you can use the proper solvent which makes a big differ= ence compared to gas phase values.
If you use HOMO and LUMO energies t= o estimate redox potentials you have a couple of issues:
1) It depends on t= he density functional what values you get. With most functionals negative o= rbital energies are way off IPs and EAs. You have to use range separated fu= nctionals to get reasonable values (Salzner, U.; Baer, R. Koopmans' springs to life. J Chem Phys 2009, 131= , 231101).
2) You can not get adiabatic IPs and EAs. I think electrochemist= ry is rather slow and you should use adiabatic IPs and EAs.
3) You can not = include solvent effects because orbital energies do not respond to solvent = effects. It is possible to use tuned range separated functionals and to tun= e them in the presence of solvent, which seems to work (Kronik, L.; K=C3=BC= mmel, S. Dielectric Screening Meets Optimally Tuned Density Functionals. Ad= vanced Materials 2018, 30, 1706560).
Therefore, I recommend to use the delt= a SCF method which gives reasonable results with most density functionals.<= /div>
= Best regards,
Ulrike

Prof. Ulrike S= alzner
Department of Chemistry
Bilkent University
06800 Bilkent, A= nkara


On Sun, Jul 14, 2019 at 7:34 AM Mo Fateh m= o.fateh+*+yahoo.com <owner-chemistry(~)ccl.net> wrote:

Sent to CCL by: "Mo=C2=A0 Fateh" [mo.fateh : yahoo.com]
Dear CCL Members,


I am working on the modeling of Organic photovoltaic cell for the first
time. I am confused:

1- Is the energy of HOMO and LUMO extracted from DFT (ground state) or TD-<= br> DFT (vertical excited state) calcs? I want
to compare the HOMO and LUMO energies with those estimated from cyclic
voltametry technique.

2- When I should use the energies of HOMO and LUMO of ground state and when=
I should use them in the excited state molecule?



With thanks,
Mo



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