Multiwfn forum

faiz1972

Member

Registered: 2018-09-12

Posts: 4

EBE (Exciton Binding Energy)

Hi Professor,

I already compute the Exciton Binding Energy of porphyrin molecule with Multiwfn. Why is the result very high more than 3 eV? According to the theory, the organic molecule EBE is about 1 eV.

Best regards
Faiz

Last edited by faiz1972 (2018-09-12 05:25:24)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,468

Website

Re: EBE (Exciton Binding Energy)

Dear Faiz,

There are different definitions of excitation binding energy. The value produced by Multiwfn is Coulomb integral between hole and electron, while another popular excitation binding energy definition is IP-EA-E(optical gap), the two values are very different.

Tian

faiz1972

Member

Registered: 2018-09-12

Posts: 4

Re: EBE (Exciton Binding Energy)

Thanks for the information, Prof Tian Lu.
By the way, how to compute the EBE, IP-EA-E(optical gap)?
Can I compute it with Multiwfn?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,468

Website

Re: EBE (Exciton Binding Energy)

E(optical gap) corresponds to the lowest excitation energy, it can be calculated via e.g. the popular TDDFT theory. For example in Gaussian, you can use such as "PBE1PBE/6-311G** TD" keyword. The geometry should be firstly optimized at ground state.

IP is vertical ionization potential, it is defined as IP=E(N-1) - E(N), where N is the number of electrons in neutral state, E is single point energy. Therefore you should perform single point calculation for neutral state and cation state respectively. The geometry should be firstly optimized at neutral state.

The EA is electron affinity, which is defined as EA=E(N)-E(N+1), it can also be easily calculated via quantum chemistry codes.

More information about this definition of exciton binding energy can be found in Mater. Horiz., 2014, 1, 17–19.

faiz1972

Member

Registered: 2018-09-12

Posts: 4

Re: EBE (Exciton Binding Energy)

Thanks Prof Tian Lu, but I am not used Gaussian.
How if use Orca?

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,468

Website

Re: EBE (Exciton Binding Energy)

Thanks Prof Tian Lu, but I am not used Gaussian.
How if use Orca?

Any mainstream quantun chemistry code can easily calculate that quantities.
There are many examples in Orca manual, please just follow them.

faiz1972

Member

Registered: 2018-09-12

Posts: 4

Re: EBE (Exciton Binding Energy)

Thanks Prof Tian Lu, but I am not used Gaussian.
How if use Orca?

Any mainstream quantun chemistry code can easily calculate that quantities.
There are many examples in Orca manual, please just follow them.

Okay Prof, Thanks very much.