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**faiz1972****Member**- Registered: 2018-09-12
- Posts: 4

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)*

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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

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**faiz1972****Member**- Registered: 2018-09-12
- Posts: 4

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?

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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.

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**faiz1972****Member**- Registered: 2018-09-12
- Posts: 4

Thanks Prof Tian Lu, but I am not used Gaussian.

How if use Orca?

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faiz1972 wrote:

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.

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**faiz1972****Member**- Registered: 2018-09-12
- Posts: 4

sobereva wrote:

faiz1972 wrote: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.

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